No idea what these plugs look like or size wise, but would those little plastic/rubber feet things you stick under electronic stuff like modems etc do. They might do and perform better than foam rubber???? Just a thought.

Maybe, I'm not sure that those rubbers would have as much give in them as the original rubber but perhaps that wouldn't matter anyway. I pulled one of the assembly's apart last night and managed to polish the plate with the rubbers up without damaging the them. Just gave them a hit with mill wax and they come up pretty good. I was worried they'd be close to perishing but they there still in good shape. Hopefully the other bank of targets comes up ok to. The rest of the metal parts will go of to the electroplaters for re-zincing.