Couple of possible solutions:
1. Trace around the existing POS then have a glass shop cut a replacement from a glass mirror and attach it right over the existing 'mirror; with a good 2 sided tape or even glue.
2. Buy a chunk of this mirrored plastic and again, attach with 2 sided tape or glue:
https://www.amazon.com/Acrylic-Mirro.../dp/B01MXE417D
All you will get from Keystone (or any other RV mfr.) is more of the same
The mirror on our '14 HC343RL is still good (I think) but as another has said, only used when I check for leaking sticky red stuff after whanging my head on the BR slide or the king pin (which I did bloodily on the last and SOB)