Shopping for Wheelchairs

I bet that very few of you have tried shopping for a used rear wheel drive wheelchair. After our power soccer clinic on Sunday, it became incredibly obvious to me that rear wheel is the way to get more power. Not that I would automatically rise to that level just because of a new chair, but I would have the potential to raise my game to a level where I could be competitive. I have never been on the market for a used wheelchair before, so this is a bit of a new experience. However, it seems as if there are very few power soccer caliber chairs on the market. Most of the chairs are either mid-wheel or the portable type meant for people who don't need to use their wheelchairs all the time and want to fold them up. So, I just throwing this out there, but if anybody knows of a website with a good inventory of tilt wheelchairs, please let me know. I think that some people have to be selling, and I just need to find them. In fact, I will be selling my backup as well once I find a rear wheel chair. If anybody has any good leads, please let me know.