After reading these I remembered what the new Beetle owners found to be able to put old VW hub caps on their bugs to get that retro look. They are clips that were used on old 50s VW buses to hold on the caps.

here is a thread on the nb site about them
http://forums.newbeetle.org/showthread.php?s=8baf3872c92f3599e39faaeb45d750f7&threadid=25368&highlight=hub+cap+clips
here is were you can get them.
http://www.bfyobsoleteparts.com/volkswagen/product.php?productid=1501&cat=0&page=1