I know that catsailor sells complete cat trax and some parts but I figured out a way to fix old cracked roleez wheels used in a lot of the trax (and probably works for other types as well). The set I got were old and one of the wheels had cracked and this let air out despite trying all sorts of glues and tire-sealant. I tried one last effort- I drilled a hole in the tire, let as much air out as possible and squirted in 2 cans of expanding foam insulation/sealant (from hardware store). It works... and beats the 100$ replacement cost. HOWEVER, I encourage everyone to support catsailor 
I think I've heard of doing that before....and that that foam tends to absorb water. 
yeah, it might... but we'll see. by the time I just give up and buy a new wheel I will likely have already spent more than the 100$! But hey, whatever works... gives me something to do when I am not sailing
I had a tire that was leaking too. I filled it with air, and submerged the tire in my pool and you could see the air bubble coming through the cracks. I spent $28 on a tire tube from an ATV / Lawn Mower shop. Took me all of 10 minutes to install the tube. Trax are like new. I filled the tire and haven't touched it, including adding more air. I'm on my second year.
well... CORRECTION! The split in the tire was taped with duct tape but when the foam worked so well I took the tape off.. bad idea... the foam expanding split the tire along that splt. looks like I over thought this one.