The rubber mandrels that come with the Rio Grande kits are great. They are flexible enough to give you needed control. I have not seen them from any other source after a "pretty" good search. I can order some if you don't want to go through the hassle setting up with Rio Grande and ordering their $10.00 catalog. The item number for the mandrels is 337-234 @ $10.95 for a pack of 3.

I should say that I have found it tempting to focus on a pitted area, thereby creating a low spot on the surface. This won't show up until you are putting a mirror polish on the blade if that's your intention. The result is a shiny but slightly wavy reflection like a carnival mirror. As Bill states in his CD, each step is critical to the finished product. It's also critical to use every safety precaution available to you. That means, eye protection, masks, gloves, etc., and using the proper rotation relative to the edge.