I never heard the trail pros having a leaking air issue. My uncle had a set of them on his 85 or 86 Honda TRX125 and that thing went everywhere, mud, snow, upside down, you name it. Eventually the spines in the hub gave out and he drove it with only 1 wheel spinning for a few months before he welded the hub on. He had that machine 15+ years with the same set of tires on it. They are very stiff and heavy, but longevity they last forever. The only way I've ever seen a set worn out is from people driving on the road a lot.
I'd rather have trail pros instead of these.... I have like 4 or 5 sets of them anyone want to trade xD. Horrible tire for a 3 wheeler unless it's under powered or you never slide the rear end around. The one machine with the odd ball tires I got the tires super cheap new $100 for the set so couldn't pass them up, machine came with OEM tires dry rotted to death.
As for
parts, I always check a dealership site like partzilla.com if it's in production yet, if not jump to ebay. If you have the room, it never hurts buying a 2nd machine for
parts and is generally the most cost effective way to stock pile
parts.