The mic/pre combo @infovore posted is available as the cortado, which seems to sound really great.
The Cold Gold pieces are real inspirational in terms of form – their idea to solder an alligator clip onto the mic yields some incredible results, and their hydrophone is awesome. (a friend has been recording the Hudson River thawing and freezing, and the results are wild).
When I was building contact mics in college, we would get “liquid tape” or “plastidip” and coat the mics so they would be waterproof, and a little more sturdy. The piezo discs are notoriously brittle, so reinforcing them can be helpful, especially if they’re really thin. Some of them are mounted on a thicker brass backing, which is sturdier but still not hard to bend to the breaking point.
My favorite contact transducer EVEERRRR is the Barcus Berry. These things are so incredible. Transparent and very sensitive. Not waterproof, which is a shame, but you can work around that if you want to.
My friend Kaori Suzuki did a recording in the San Francisco Bay of a flagpole in the wind, and it was sticking out of a dock that rose and fell with the water. The chain clicking against the pole made these incredible laser sounds, and the dock scraped and squeaked against the base of the pole. Super beautiful piece.