Midway USA and Buffalo Arms has about any caliber you might want and they have them in two thicknesses, .030 and .060. I know they have been used mostly for blackpowder, but after reading the wax gas checks thread, my little mind got to thinking, "hey, I bet these work with smokeless loads as well." It's a pretty easy gas check to use and if they eliminate leading, I'm all for it. I think they would be especially helpful for .45 Colt loads in revolvers with large chamber dimensions, I think, anyway.
Steve