Give KSI Enterprises a call.
1-920-788-0220
I personally haven't purchased a clutch from them. But looking around they appear to have pretty good prices on new ones.
One other thing. If you are looking for specific parts go the Arctic Cat parts lookup. Look for primary clutch parts for a 2000 800. They will have a break down of all the parts to build the clutch. Where as if you look at the later years they have components for sale but not the little things like rollers, buttons, etc. Something to try. I think you can get a movable sheave and spider for around $225.
Thunder