Apple doesn't release cases. They are all from 3rd party companies.
Have you tried eBay? I've seem some clear cases there.
I wanted a clear case but I got
this one. (the eco-shield) It's off-white but it's a hard, very form fitting plastic and it works with the universal dock. It is too thick to work on the iPhone dock or the dock that came with the 3G iPod. (I've tried both)
I really like it.