I also looking for the metal bumper right now, I searched from the web, not many website selling this, and I got this website
website looks comfortable, I'm now looking for the reviews of this website, so far the reviews are good, quick delivery. I'll keep an eye on this site.
seems the bumper cases for iPhone 5 on e13ctron for preorder only
and the iPhone 5 cases on groupcow.com are all instocks.