Where to get replacement Rubber Feet?

here is something I found at partsexpress:
Penn-Elcom F1633 Rubber Cabinet Foot 1-1/8" Dia. x 1/2" H
Search the partsexpress website under speaker building or do a manufacturer search under Penn-Elcom.

Also, have you considered vibrapods or Herbie's Audio Labs products. Herbie's website is a good read. I am using the big fat dots (9/32 in. thick) under my heavy monoblocks, and previously used them with success under large speakers on hardwood floors.

Try Antique Audio Supply on the web.

Your local Ace Hardware store.