found a source for mirror glass *LINK*
john lucas
This place sells them at a decent price. Not the quality of the glass I had before. The glass is a little thinner and the bevel is not as wide but for all practical purposes it's very good and the customers won't know the difference. The first batch was dead on 4". From the other company every batch I got was a slightly different size so maybe this will be a good company to stay with. They have a parent company that will sell wholesale. Not sure I want to go that route again but will look into it.
http://www.collectingwarehouse.com/Product-Home-Page/Round-3mm-Beveled-Glass-Mirrors/Beveled-Glass-Mirror-Round-3mm-4-Diameter.html