We successfully used a Teensy control board as our custom interface board. It was pretty easy to setup. (
http://www.chiefdelphi.com/media/papers/2666)
Any push button will work as the buttons, we bought ours from a local electronics store but Mouser.com, digikey.com, sparkfun.com or any other online retailer will have the same thing.
10k potentiometers work well with the Teensy, remember to get linear and not audio taper pots. Again most electronics suppliers will have them.
Let me know if you have any specific questions about building the panel.