Hello Belanna,
If you are using EcoInvent, i would recommend looking for the processes called zinc coating (coils or pieces). They represent the hot dip zinc treatment. You can investigate the amount of zinc used per m2 in the process, and convert it to the amount needed.
Furthermore, it should also be possible to find EPD's on galvanized steel products, that you can use as a proxy, or a comparison.
Best of luck in your search.