Is the mirror glass the same size as the 71 and 72 F-bodies? If so, Paragon Corvettes sells the replacement glass under a Corvette application. I swapped out mine fairly easily using very hot water to soften the gasket that holds the mirror section in.
https://www.yenko.net/ubbthreads/ubbt...pics/487291/21
https://www.yenko.net/ubbthreads/ubbt...pics/487291/22