Try dirtcheapsnow.com They are the cheapest I have found for oem parts. I just bought some SS valves for my wifes sled. They were right around 75.00 each for the valves
1) Clean your exhaust valves AND bores, their dirtier and gummier than you think. While you're there check the bellows for small rips and tears.
2) The original exhaust valves are aluminum, which were prone to failure and severe engine damage could result. Then they went to titanium, and the latest and greatest are Stainless Steel, identifiable by the heavier weight and "relief cut outs"
3) The original exhaust bellows were blue, the latest and greatest bellows are Orange in color.
4) POLARIS part # 2202838 (order two kits, it's only enough parts for one cylinder) includes stainless valve, orange bellow, and 1 exhaust spring.