The Seac shafts should work, too.
There's a shop on Frederiksberg, I think on H. C. Ørstedsvej that carries Seac, but I don't know if he has extra shafts for pneumatic guns. I once bought some spare sets of o-rings from him, though. The name escapes me though. But it's on the left side, just before the gas station just prior to the Danasvej intersection, I think.
Keep in mind that the cheaper 8mm galvanized (?) shafts that often ship with the lower priced, non-vacuum muzzled guns may not be a good fit for you. I suspect they will pit and wear out the muzzle seal in the Vuotu vacuum muzzle very fast. And yes, get some spares of those.
I know mechanic and machinist is not the same but perhaps you have a friend on someone at work with access to a lathe? If you do, you can buy pretty much any shaft you like for bandguns as long as, once cut at the most forward sharkfin (or notch) it is still long enough for your use. Then cut a thread at the rear of the shaft. I posted the dimensions of the thread in another thread, but you can just make it the same as in your original spear. BTW, if you need to take of the tail end on your current shaft, it might be loctite'd in place so heat it up and be careful not to mar the tailend when you unscrew it - that can also shorten the life span of your vacuum muzzle seal.
But one mechanic's trick; if you need to service the gun, no need to buy oil from Salvimar - just use some suspension oil (like the type in motorbike forks). Something not too thick. I think the Italians recommend 10wt (or whatever the designation is).
I have recommended
www.edosub.it to others here before and everyone seems to have as pleasant experiences with him as I did. He has fair prices and knows about pneumatics and carries pretty much all spare parts. But I am not sure you need enough to warrant shipping cost though it may not be that high just for a bag of extra seals, a few sliders and tailends and a shaft.