Replacement of day/night mirror glass

The glass in a day/night mirror is wedge shaped in cross section; the front and back aren't parallel as in a normal sheet of glass or mirror. In the "day" position you are looking through the front surface at the reflection off the silvering on the back surface. In the "night" position the silvered back surface is pointing up at the dome light so you can't see it from where you're sitting, and the dim reflection you're seeing is off the front surface of the mirror glass. The wedge-shaped glass isn't available as a repair part. But day/night rearview mirrors in good used condition are not hard to find.