if your windshield is like the one on my Four Winns, its made by WaterBonnet... I dont know if they are still in business, but if they are, maybe try contacting them and see if they have any options. Boat windshields arent known for changing a heck of a lot over time, so you may get lucky.
if they are defunct, you are stuck trying to find used glass that will fit that is in better shape or keeping what you got, and being happy with it.