It doesn't matter how hard the trick is to perform, it only matters how amazing the effect is on the spectator. My dad is the exact same way that this guys' uncle is, and I pulled out an Invisible Deck and fried him.
I think that I'm going to have to go with Double Facers and Double Backers. I think that after you show an Ellusionist style gaff card, people are going to have much higher expectations of you, and unfortunately, some can't live up to it.
There are a few places to get Tally's in bulk online.
www.filmart.com
www.batteriesandbutter.com
I would get from whichever store offers better shipping to your area. I live in PA and the warehouse of BatteriesandButter is in NY. I got 24 in 2 days. :D