Heck, I don't have any idea of a number, but I know I have several collectible Colt Pythons that are unfired. At least one of them supposedly has never even had the cylinder turned.
I have quite a few Pythons that are not NIB, but I will probably not fire them either, just because of the collectible nature of them. Some of those models only had a total production of 250 of them.
I can only think of one rifle that I have not fired, but it was bought used, and it's just that I haven't taken the time to sight it in after mounting a new scope on it.