I'm having a devil of a time trying to find one... the plastic "universal" one from Ebay just plain doesn't fit.
I know there's the cast aluminum one from GM (15765623), but damn... $120?
I also ran across this sheet metal one from GM as well (15000206), but I can't find any pictures of it. It's way cheaper, but I'm hearing it doesn't utilize all the bolt holes on the dust cover flange on the transmission.