I just ordered some stuff from TVI, and they had everything I wanted. Granted, I didn't want much, but it was more than most places seem to stock.
ATV dealers seem to play by the rules of auto dealerships where everything is ordered. It works for cars because people don't work on their (new) cars much. I wish ATV dealers were more like farm equipment dealers. My John Deere dealer seems to have about any obscure part you could ask for in the back room!