Congradulations on getting an ATK. If you like XRs, you should love it.
Two good sources for parts and such are:
Keith at ADB. He is a weath of knowledge on the Rotax models, and can supply lots of parts. http://www.americandirtbike.com/
Dan and Motoxotica stocks a surprising number of parts and can get them to you super quick. http://www.motoxotica.com/
Also check out the ATKRIDER forums.
I have a '97 and love it.