The glass is somewhat unusual in size (5" x 7").
There is a company called "K Source" which manufactures many aftermarket exact replacement door mirrors and mirror glass, and sells through the major outlets such as AutoZone and O'Reilly's. I wrote them, and they seem to have very good customer service, so I am hopeful they might have it.
Alberto with K Source has been extremely helpful so far. He asked me to send him a picture of the mirror so he could see the exact shape of the glass, and promised to check all their mirror glass offerings for a match.