Mine are made of maple I have cut off of stock blanks, that I have lined with spare leather that I picked up from Tandy when I made a shoulder holster for a pistol I regularly carry. Cork could be used, but I think you are right and it would probably get chewed up in not too long. I have never replaced the leather on my wooden pads. I merely stuck it to the wood with spray adhesive, and screwed the wood to the metal jaws of the vise. So far, I have no complaints... It holds the stock without marring the wood.
Matt