I was poking around a while ago and found this company. It looks very much like what’s in my ND.
Industry-leading global automotive supplier of innovative, advanced technology that optimize driver vision and enhance driving safety and convenience.
www.gentex.com
I haven’t done any more research beyond finding the website but if it’s not cost prohibitive and available to the public, it might be a good option.
FWIW, My experience has been that a roof mount is the way to go. I’ve driven around in the ND this winter where the rear glass is completely covered with snow or mud but the rear view camera is unaffected. I have noticed that rain doesn’t really affect the view. Snow obviously has to be removed, as well as, when things ice over but gently removing ice from a small lens is much easier than scraping away an entire rear window