I got this one from amazon awhile ago.
It says it costs $40, but I don't remember it being that much when I bought it. It's a really good tamper, but probably you find just as good at a better price, depending on your needs and budget.

I bought this one for my GCP and was really impressed with the quality, especially given the price. The metal part of the tamper is machined very smooth and to a really tight tolerance. Works great!