The gaskets for the lower intake? You're doing those too? Is something else wrong?
For the SC outlet gasket, just go to the dealer. Mine was 12 bucks. I don't know the number. Don't forget the 2 little o-rings for the coolant passages between the lower intake and the SC, and don't forget the injector O-rings, either. Buy that set from the dealer too. By the time you order and pay shipping on these cheap items, gmpartsdirect isn't that great.