[Backstory: Over on the Cigar Box Nation forums, one of the guys asked where he could buy radial volume labels for an amp he built. This is a slightly edited version of my reply to him.]
Why buy some when it's easy enough to make your own? You don't have to be good at graphics, you just have to know what to do.
Download Inkscape (you probably want the Windows installer) and install it on your machine.