Some plastics supply stores have it, most larger cities have plastics supply stores. Locally to me, you can walk into a Port Plastics and buy it. You would need to call or check out the websites of plastics suppliers local to you.
I knew you can get it online. I was just trying to get some to work with this weekend. I'll just build up a temporary cheek rest like the one I have been using until it comes in.
My plan is to mold it and attach it to the stock with the industrial grade Velcro. Do you guys thing k that would be stable enough?