Bill, try Art's Parts in Cornell Wi. (715) 288-6863. They deal in new and used parts for snowmobiles, motorcycles, ATV's, lawnmowers and just about all other toys except boats.
Mills
Don't they sell them through somewhere like www.DennisKirk.com? or Pat's Small Engine, He's online also, do a google search. I thought I've seen them before at on of those two places. I was going to recommend Port Yamaha, I've always liked buying frm them. But if you want to try an aftermarket, then try one of the 2 I mentioned, I've bought from both of them before.