[villagetinker]

If that is a glass overlay, then the big box store as well as ACE have glass that can be cut to size. If this is actually a mirror (could not tell from the photo), there are some glues that work very well on glass and MAY fill in the cracks so they are nearly invisible. There would be some clean up after application. These are similar to 'crazy glue' and come in liquid and gel types I suspect the gel will work better and give you additional working time. A razor blade should remove excess glue, and acetone if absolutely necessary. I would cover the repaired mirror with glass so as to avoid future damage.