When you order the trick, you'll get 20 gaffed cards (20 performances).
Refills are available in decks of 52 gaffs.
At the moment, the page for the single deck refill has been removed from earlier today(the pricing was incorrect...PM is fixing it ;-)
However, the 'bargain' 3 pack is still listed.
http://www.penguinmagic.com/p/8339
PM confirmed this info when they shipped my orders earlier today.