Hiya
The Rabitech Pelagic reel is constructed from glass reinforced nylon. Very solidly built reel. The nicest thing about it is that it will work well on guns under 90cm's, as the reel is neutrally bouyant. On smaller guns, many will sink with the spear out of it when a reel is fitted to it. Mine holds about 100 yards of 3mm line.
http://sumora.com/shop.php# Chat to Erik, very helpful and knowledgable guy!! Sure he'll be able to assist!!
The Omer Pelagic 100 is made from aircraft grade alluminuim. Very robust construction and will also hold about 100' of 3mm line. I have one fitted to my 115cm Rabitech Carbon Apex and its my favourite set-up!!
http://www.omerdiving.com/catalog.aspx?category=9 Drop Mark Labocetta a email or pm. Another very experienced spearo and a very helpful guy!!
The Rob Allan reel is made from stainless steel. MUCH thinner and lighter than the Omer Pelagic. Also holds about the same amount of line. This reel is made to be mounted horizontally, whilst the other two are made for vertical fitment. My 120cm Carbon RA has one on, and it also works very well!!
https://www.flfreedivers.com/ Speak to Mike Damms. Yet another very helpful and experienced spearo!!
Another option is the new Aimrite reel. I don't own one, but from the picture's and Aimrite's reputation, its will work brilliantly!! I'm sure Bill Mc. will chip in to give you a detailed review of his aimrite reel, as well as all the others!!
http://www.aimritehawaii.com/accessories.php
Sadly though, no matter which reel you acquire, you will still have to drill holes in your barrel!! All of mine were done by the manufacturers, and i can give you exact measurements of how far back to drill the holes, so as not to damage the barrel plug!!
Regards
miles