You can get the Pro-Clamps at www.sixstardj.com a couple bucks cheaper. I also found aluminum clamps at Home Depot made by Halex for only $5. They didn't have the size I needed though.
A company called Halex makes an aluminum clamp (part# 51320) that I put on my 2-1/2" tower. It fits snug,but it works. And it's only about $5. Home Depot is getting rid of that clamp, but a few still have them.