[Dacious]

A good source for the springs is the old Birko type jugs where the element is bolted to the top of the ceramic or plastic jug and dips down into the water inside. I haven't looked in years, but hardware stores used to carry the springs as a replacement for a few cents/pence.

I even have a book full of electronics projects which shows how to make a spring reverb from these along with record player stylus magnetic cartridges.