I went to Autozone to get a new backplate gasket for my water pump and the guy told me that no one sold those and that I would have to buy a new pump Is this true?
If not where is a good place to get new ones, or should I just use silicone?

he's right you need to make your own gasket ,with gasket material and take a hammer and tap out the outline of the pump
on the gasket then take a razor knife and cut it out or use holamar or honda bond silicone to stand the pressure