You might have a look at old home organs too. The sproingiest spring I've ever come across was in a Yamaha BR-30 (I think that was the model) organ from the 1970s. I modded it to include an effects send/return, since the organ had an internal amp and a choice of 1x12" speaker or a single horn rotary speaker. With a soft drive pedal plugged into the effects loop and the reverb turned up, you could make the nicest chugging reggae organ stab sound I've ever heard. A large part of that sound is the spring's reaction as a overdriven stab hits it and makes it resonate. It had a long reverb tank, but I don't think I took it off so I don't know how many springs it had.
Tom