Jim, I am afraid you are in for a tough job. It is my understanding the 41 Chevy coupe rear window is one of a kind and you are at the mercy of the NOS dealers or will have to hit the junkyard trail. Hope I'm wrong!!
I believe if you look in a parts book you will find the rear glass is the same for Chevrolet Passenger cars from 1941-48. I'm pretty sure that the coupes and sedans share the same glass, too. That being the case it should be a very difficult task to find a back glass as there are more 41-48 Chevrolets extisting than any other group of pre-49 Chevvies.
Replaced all the glass in my 41 about 5 years ago. There is a dealer in Coos Bay, OR. that has the glass and is usually a vendor at most of the bigger NSRA shows. Right now I can't recall the name of the company but at least that will give you a place to search.
The coupe and sedan rear glass are not the same by the way.