I'm an Art Teacher in Tennessee. I've got a whole grade level of second graders, about 150 or so kids. They are working on "mini" artist's trading cards right now. That's a size of card which I invented when we started running low on cards. I cut them in half, measuring 2.5 inches by 1 3/4 inches. My students are all making zentangles, but I'm not picky about how the ATCs are decorated. It would be great if they are all that mini size, but if that is not do-able for you, let me know.
Here's a link to the swap if you're interested! http://www.swap-bot.com/swap/show/140282