Oh, derp. Somehow I missed that you were looking for a case. Do you mean a storage case, or something to carry the laser while you're out and about?
If the latter, galls.com sells various flashlight and baton holders that would fit an extended C6. Not sure if they are the cheapest site, but they sell quality gear and were always easy to deal with, years back when I was working in security.
Would something like this work?
Galls flashlight / baton holder
It has a loop on the back to fit over your belt, although I will point out they're mainly designed for 2" wide duty belts. I still have my duty belt, and I'm almost tempted to get a few... when I go out for a walk at night I carry anywhere from 4 to 6 lasers, and they can be a pain to carry if I don't have enough pockets