hey man, i see you're going to build a guitar, thats great!!! i can't wait to see the finished product!
actually for my transducers, i dont' have a standard supply, i strip them from where i can. my last few guitars used the piezo speaker elements stripped from some $.99 toys in the dollar tree. i had good luck with small keyring "personal alarms" which have the pull tab and sets off the siren. the speaker in those works well for me, just superglue them to the inside of the resonating face of the guitar, and wire up each lead to a mono jack. there's really no smoke and mirrors to my stuff, i've just had to keep working to get the best out of the least, ya know? lol keep me updated man!