Found replacement parts I couldn't find elsewhere.
I found the website easy to navigate and find what I want. I decided my son would be more comfortable if his wheelchair had pneumatic tires. I had been looking on various sites with no luck. I easily found them here. They arrived quickly and I installed them right away. My only suggestion is that you list the inside dimension of the bearing, which is where the axle goes in both SAE and metric. It was listed at 5/16" and it threw me at first because I'm pretty sure everything is metric now and I had measured the axle at 8mm. Turns out 5/16 is 0.31" and so is 8mm.