If you have a power band saw you can cut the hockey pucks into strips that will fit
As well, you might look for the replacement heads that are made for a small mallet instead of cutting up a good tool.
Back when I lived in San Diego (around 1992)I replaced my original rubber stops. I found a a business that sold rubber in the yellow pages. I took one of my old peices in. The guy hacked off a couple of new ones from some rubber he had in the shop. I think I paid less than $5.00 at the time. What ever kind of rubber those were made from - they are still on the boat