Thanks everyone for your suggestions.
I talked to one glass shop today and they were not interested in trying to make a new one.
I guess I'll try to get one from a dealer. I hate to spend that much for a mirror but I'd rather keep the original look of the tractor.
You are right George, freezing is not really a problem here but heat may play a role. I could kick myself in the rear though, it had fallen out once before but didn't break, I put it back in using just the original rubber seal. In hindsight I wish I had done something like you did to make it more secure. I will do that for the replacement and might as well do the left one too.