Not sure if you're talking about a case badge or not, OP. Case badges are ~1" square, used to be placed on the front of the case, usually in the vicinity of the power switch.
If that's what you're looking for, try
BestByte (do a search for badge), or
Directron.
Otherwise, the only decals I've ever seen are full case decorations. Not sure where you'd find those. Or laptop decals, which you should find with a simple google search.
Hope that helps! :biggrin: