I could not find a dumb keyboard to buy, so I made one using stiff cardboard, a rule, pencil, fine marker, thick marker, and exacto knife. Very low-tech, but it works!
If you do this yourself, I recommend a square as well — to make good right angles. You can take measurements from a real piano, or look them up on the internet. I did the latter, since I was away from a piano when I decided to build the dumb keyboard. You can get all the supplies you need at an art store. Oh yes — you need a good cutting surface or you will be in trouble with someone:-) Art stores also sell nice cutting mats if cutting is something you will do regularly.
zipTimer: an iPod/iPhone app for pacing piano practice, cooking, workouts, you name it.