They are not easy to come by. I don't know if you could this year, but previous years, you had to get it through the race dept. Try Goodwin's - they had some cut for 800 Etec's in the past for purchase
If you are looking to go that route, you may also want to consider a P85 with a doo taper cut into it - might save you a few bucks. I've used both P85 and Yamaha primaries in the past with good luck on both 4S and 2S 800's
If anyone can find you one try Darryl Baker at Racers Edge. He used to sell alot of the TRA race clutches for his builds from the race shop. His number is 403-254-8686