Hy 1958GMCnut, good luck on your search, I think you may find some covers, but I seriously doubt you will ever find S.S. ones. Please keep us informed on what you find.
I found a place in Texas that would make the SS lugnuts (do yours have castellated ? sides with tight "slits"? - expanding hex locknuts?) for about @$5 (that was two years ago - the price might be doubled by now).
I'll also be watching for someone who posts a source.
I don't think you'll find either in SS, and in our climate it's a bad idea to use the covers unless the truck will never see wet roads, them things are horrible to get off once they start to rust on
