If you are adventurous, and like to tinker, "Livid Builder" is a line of Do-It-Yourself parts that make it easy for makers to design their own physical computing devices and MIDI control surfaces using buttons, knobs, encoders, velocity pads, arcade buttons, accelerometers, faders, other sensors, and LED’s.
http://www.lividinstruments.com/hardware_builder.phpMidi Botique also sells kits
http://www.midiboutique.com/products/products.htmAnd also this site
http://store.highlyliquid.com/collections/midi-controllers/products/midi-cpuDuane