I think you're talking about a tuner piezo pickup. It's a pretty simple little thing, freely available on this side of the planet.
I got this one at a local music store here for about 12 bucks, same price they're asking on Amazon.
http://www.amazon.com/Matrix-MPU2-Cl.../dp/B0002F4TQO
FYI - I was never able to really get a good grab on my bridge with this. It didn't seem to open wide enough - I basically bought it to tear apart and make a homemade bridge pickup from anyway, and it worked reasonably well (for 12 bucks) for that.