Misc.

Theremin schematics
http://www.maxiespages.com/theremin/schematics.shtml

Piezo Disks
Richard Lerman - look under schematics for advice on wiring disks and building a preamp for piezos.
http://www.west.asu.edu/rlerman/
http://www.west.asu.edu/rlerman/PDF%20Files/Audio%20Schematics2.pdf

raw disks:
http://www.allelectronics.com/
catalog #pe-33 1.5 " disk

Premade sturdy contact mics:
http://www.kksound.com/
try the "bigshot"
http://www.windworld.com/emi/