I don't know about the steel gears but if you ever need replacement parts for your buggy go here. http://imexrc.com/SearchResult.aspx?CategoryID=95 They have pretty much everything you could need for the xrc. You could just buy a whole bunch of plastic gears from them if you can't find any steel ones and replace when they break.
If you can pull off the spur gear and maybe take a good photo of the back of it we may be able to help you, you may also need to measure some things to compare them properly. I'm pretty sure I read that the FG gears fit the XRC on roads so hopefully you'll be lucky and it'll be the same for the offroads.