Tauruck
Check out Allmetalshaping.com. Search for info on "FSP" flexible shape pattern. It is used to duplicate shapes. We use it on metal but there is no reason the procedure couldn't be used on glass. If the fsp is done properly, you can tell very small variances between the two shapes. For mirror images just turn the pattern inside out, same shape reversed.
edit: Google, flexible shape pattern, shows much.
Ron