"So what's left? What material would you suggest they could use?"

Type III Hard Anodized Aluminum, not the thinner, weaker Type II they apparently used. Also, a little more texture on the back would have disguised scratches better.

I carried this HA III flashlight on my keychain for years with surprising little wear, given that it's constantly scraping against keys, key rings, and other metal tools. http://www.arcflashlight.com/arc-aaa.shtml