I spent a fair amount of time this week looking for black mounting screws to match some original JBL hardware. I couldn't find a local source, but was able to find a cheap and plentiful substitute.
I bought some shiny zinc plated screws at the local hardware store and gave them a quick treatment of gun blueing. I had the gun blue in the cabinet, but you can buy it at most sporting goods stores. The chemical is selenium dioxide. You apply it and the screws immediately turn a nice black. I dried them, and gave them quick shot of wd-40 and they look just like the originals.