First of all, Welcome! And congrats on the gun, it will serve you well.
Where To Buy
Now, for your parts , I would recommend getting everything from the knowledgeable Edo at
http://www.edosub.it/. His website looks a bit old school but he has everything you need and knows more about pneumatics than most other shop owners. He ships fast, packages it nicely and wont sell you stuff you wont need.
There is another shop nearer to you, that I used to recommend but twice has that shop now shipped out later than they promised (and then denied it) so I can't really get myself to put them forward any longer. Finally, there is Scubastore but while they are cheap, you can never trust their estimated shipping times. If you order more than just 1-2 items they are notorious for taking quite a while to ship out.
So, my recommendation will have to be Edo. He is fast on email, too and his prices are actually very competitive and you get the satisfaction of having helped a small shop exist in the "Walmart World";-)
Shafts
Get Devoto Sub or Sigalsub. They are made out of stainless 17-4ph and probably equally good. Edo carries both. Popgun Pete will prefer replaceable tips but, personally, I would get 7mm tahitian shaft (no screw in tip). These will be the fastest and most precise which I fin preferable knowing that most fish in Thailand will keep a bit of a distance. I would just get two shafts.
I have two guns in your size and have shot their shafts into reef a bunch of times and still haven't managed to bend any of them. Both are still using the first 7mm Sigal shaft I got for them (come to think about it, the only tip I have actually bent was a screw-in one - it was the stock one that came with the galvanized metal shaft of my first gun). Blunting the tip, yeah, that can happen, but you can file it sharp again on a rock if need be. Also, often restaurants in Thailand will have a grinding stone in the back and I have had luck borrowing those.
Measure the length of the shaft you have now and just order the same. Possibly you can even go slightly shorter but you would need to measure that carefully.
Sliders
Salvimar's early sliders were said to be brittle and break easily. Now, they should be fine, so you can get an extra of those or possibly buy a few from Tomi/Marko (look for Tomi on the forum). They are very low profile and made out of Delrin, so less brittle. Yes, you can use the Salvi sliders with any line. Tomba sliders have quite small holes, so if your mono is too thick you can't fit it through, but then it would be too thick for performance reasons anyways.
Line
Do not use monofilament on the reel, use some dyneema. It is hard to find a dyneema that works equally well for the reel line and as a shooting line, which is why most people use mono as a shooting line (from spear to reel line). 1.3-1.6mm mono is fine for you gun. Do not go larger, it will just have more drag. If you really have to, in a pinch, you can use the dyneema on the reel as shooting line, also.
But you can also decide not to use the reel at all. But then you really should get a float, see below.
Crimps and Crimping Tool
It is kind of annoying having to travel with a crimping tool/crimping pliers as they are a bit heavy. But it is the safest way. Alternatively, you could rig both your spears at home with mono and then you might not even have to change out the mono on your travels. Just change the spear if you cut the mono badly on the first spear. If you wear both of them out, then you could use dyneema from the reel, but it is not ideal. Or you could always tie mono, you probably know much better than me how to make nice, low profile knots.
BTW, don't pay more than E20-22 for a crimping tool. That's still more than twice what I pay for OK quality ones in China and I suspect all brands get them from here - so when I see Omer charge E40 I kinda feel sad for the customers.
Piston
Get a spare Mares 13mm piston. They are tough as nails, affordable and will work perfectly in your gun, too.
Shock Absorber
I had a few issues with the shock absorber on one of my Vuoto muzzles, but there's no need to buy a whole absorber - in all likelihood if anything breaks, it will be the o-rings on the shock absorber, so you could just bring extra of those, if you can source them cheaply. On the other hand, chances are you wont even notice if they break. I didn't until I took the gun apart. But I guess there is no harm in getting one, they are pretty cheap anyways.
Wetsuit
A wetsuit will prolong your time in the water substantially. I dive with 3mm in the tropics (Philippines, Thailand). Maybe you can get away with 1.5mm but often they aren't really cheaper. But at least you will need less weights. There aren't tons of fish in Thailand, so often you will spend 4-6 hours swimming around getting a (few) fish. It'll get cold in shorts and a rash guard. Also, a suit will protect your from the sun, coral scratches and anamone stings. You will need weights, too. But I'd probably try to rent on your location, unless you are in a place with no dive shops. That said, I do travel with lead unless I am 100% sure I can get it where I am going.
Pump
You should bring your pump, too and buy a service set of o-rings (the latter is about E5). That way, if you do have to take the gun apart, you can pump it back up. And in the very rare case you need to change an o-ring, you'll have one that fits. You need a bit of a specialty tool to take the gun apart (pump valve tool) and a properly sized wrench for the muzzle. You can make the pump inlet valve tool in a pinch on locations. I have even used a metal file once, mounted in a vice, for that purpose.
BTW, if you have to pump up your gun up, then take breaks to let it cool down. Otherwise, it can get so hot the pump seal will wear out too fast. I had that happen and a bit of rubber even got into the pump valve of the gun and got stuck so the whole gun leaked all the air I had just pumped into it. I managed to repair it, but I think I would have been OK if I had just let the pump cool down from time to time. The problem with a busted pump seal is that, afaik, they don't come with the replacement o-ring sets:-(.
Fish Stringer
Get a fish stringer to hang your fish on your belt or the float. Even if you are diving from a long tail boat, chances are your skipper wont be right next to you and you wanna have a place to put the fish. If your stringer is made with nylon line make sure you don't string fish with sharp teeth through the mouth as they will cut through the stringer and you will lose the fish and possibly the stinger, too. String toothy fish through the eyes or gills instead.
Float and Floatline
Consider getting a float, but it really doesn't have to be anything fancy. Don't buy a fancy float line either. You can get really cheap polypropylene rope in Thailand in the shops for fishermen. It floats, is plenty strong and is what the locals use. Tie that to a styrofoam ball (which you can also get locally), stick your stringer into the ball and the other end of the float line to your gun and you're good to go.
Mask
Make sure you try your mask on in a shop before buying it. Ideally, the same with a suit if you get one.
Gloves
No need for expensive neoprene gloves. Consider getting some PU rubber coated working gloves. They will last longer and be cheaper. They even make some cut resistant ones with Dyneema weaved into them.
Traveling
BTW, I have stopped emptying my guns of air before flights... Yes, it is a pressurized container but your gun probably has about 18 bar in it and a volume of 18 liters, so not really much of a bomb there compared to a scuba tank. As always, don't say you have a gun with you when you check in your gear. Call it fishing gear and no one should give you trouble. I have flown on a ton of airlines with guns by now. Also in Thailand. If you don't have a bag long enough to put the gun and shafts in, then you can consider getting some PVC pipe. But I think your 85 should be able to fit in a fin bag - my Seac 90 does and despite the difference in naming, I think the Salvimar might be 2cm longer.
