The rubber gasket is located behind the metal framework that holds the mirror in place. Sadly, it wasn't like a big rubberband. The only way I could get it off was to use a utility knife.

I looked for a convex mirror in craft stores and couldn't find anything larger than 2 1/2" which isn't big enough to fill up the hole in the center of a medallion. Then I remembered seeing 18 wheelers that had larger convex mirrors attached to their regular ones. So I stopped by a truck supply place on the off chance that they might carry them. They looked at me like I had two heads when I told them what I was going to use them for! lol