Do you want something specific or is just "WoW Themed"
Most companies that sell covers allow you to put custom images on the back. I had one made a few years ago with my character and the quality was amazing for a cheap price.

Please Help.
Thanks !

I didn't find the right solution from the internet.
References:
-http://www.mmo-champion.com/threads/2294525-Where-can-I-find-Warcraft-phone-covers
-Brand Marketing Video Examples