As MTK suggests, McMaster has material that will work. I've used their polyurethane sheet material to make replacement blocks for the DB mounts. Don't recall the durometer hardness, probably 80A. They offer a sample pack of 6 different hardness sheets you may wish to obtain for comparison to the stock blocks.

The material can be cut with a knife or bandsaw and the holes bored with sharpened brass tubing in a drill.

http://www.mcmaster.com/#standard-polyurethane-sheets/=10kcnp1