contact mic?

I guess the first question is: I am planning to put together a show
for the Acadia series in which one of the instruments will be a mic'ed
typewriter. Do you have any suggestions on how to do this? I saw
instructions for building a very cheap contact microphone out of radio
shack parts (which I'd have to order), or I could buy a contact mic
online at retail price. Thoughts on this? Or, is there a local store
to buy weird microphones from, or an electronics store that actually
has parts in stock that you know of?