I had a look at Jaco tires. They make some great rim/tire sets, but it doesn't look like anything that'll fit a buggy. Closest they do is for an RC10 truck. I don't think the trucks will use the same size axles?

I found these while searching:

http://www.tm-rc-racingcomponents.co...FrameSet13.htm

They're going to be difficult (expensive) to get here though. Still looking...