Okay, someone posted a mesage that you could use any regular game cart for a donor cart. This includes games with or without saves. But after several visits to the store, I found this is not the case.
Carts/Carts that cannot be used that I tested:
Atari 10 in one
Whack a Mole
Cart that does work for me:
New Super Mario Bros (Ironic for me, cause thats the game I needed a donor cart for. But it also works as a great donor cart for other games. I got it for $30 used from ebgames.
Prime, based on what I've read, the number of saves is based on the game that you're using for the donor card. If the game has 3 game slots. You can save up to 3 different games. It also sounds like you have to remember what save slot you used for what game or you'll end up over-writing them.