Mark, how about a thumb piano (kalimba) as the musical device?
For one that is easy to build, take a look at
http://www2.worldbook.com/features/cybercamp/html/craftthmb.html

It uses thin plywood and scrap wood for the sound box and ice-cream
sticks for the plucked tines.  (Most kalimbas use metal strips for
the plucked tines.)

Add a disk or drum with small nails or screws to pluck the ice
cream sticks.  I would extend the Popsicle sticks the other way on
the sound box to make it easier to fit the disk/drum/belt-with-bumps
or whatever actuator.

Mickey Sadler
Dublin, Ohio