I have used steel wool, 0000 grade, with a light oil to clean rust off blued guns. Copper (Chore Girl) pads would be good, I suppose. Be careful, some of those pads are said to be copper washed steel instead of pure copper. A magnet will tell you. Any place that sells gun cleaning gear will probably sell copper or bronze brushes (look kind of like a toothbrush) as well as stainless steel brushes. A Dremel tool with a cloth wheel and jeweler's rouge would work, too.