I have great luck finding wonderful frames for 3.5" x 2.5" art cards -- from the simple, clean look of a plain, smooth, black wood frame to more ornate metal and wood frames -- at Wal-Mart and Hobby Lobby. I've also found some small unfinished frames that I might actually coordinate with specific art cards, by painting the frames to match.
Just last week, I got this fabulous frame (at Hobby Lobby) that has sections that move. It's solid wood, smooth finish, painted black. It holds 5 art cards perfectly. The front two "frames within the frame" slide, so you can change which cards are displaying at whim. (Am I describing that well?)
This one will eventually be filled with belly dancers as a gift for my husband. (He's got a thing for Middle Eastern music and belly dancers, and I've been collecting belly dancer art cards by other artists, as well as making one of my own. I figure he can put the topless ones in the back section and hide them by sliding the frames around when the kids pop into his office! One more card to go! Anyone out there planning on painting a belly dancer?)
I'm surprised that other folks are having such a hard time finding frames. I live in the middle of the corn, and the highlight of this town is most definitely Hobby Lobby for me!
Jeanne