Here are a few tips on aquiring (harvesting) slot cards:

1. Always ask for two when signing up.
2. Try asking for a couple of blanks as souvineers.
3. If there is more than one sign-up place, hit each one.
4. Wait until shift change and sign up again.
5. Bring a spouse and/or a friend, or two with you; everyone sign up.
6. Search the casino floor for lost/forgotton/abandoned cards:
...Check each machine and look between/on-top/on-ledge/in-slot for cards.

Oh, and send me one from each casino, too...