A galvanized coated requires appropriately cleaning the item,
Then dipping the item in a molten bath of zinc.
While you might be able to do this in a home shop, it would be way easier finding a commercial galvanizer who runs small object thru on occasion.
While the hot dipped zinc provides a protective coating, zinc is known for “galling”, (ie. Becoming “sticky” sort of like trying to cut a cheesecake with a knife.)
The galling issue would make a galvanized coating crappy for the vise slide and opening were the vise slide travels, requiring those areas to be coated to prevent galvanizing in the galvanizing bath, or special lubricants if galvanized, to prevent galling, and these lubricants would likely attract abrasive particles to cause wear on the vise slide.
Also, cast iron is actually a decent vise material for wear areas, since cast iron has graphite and carbide elements within the iron that reduce wear. ( this is the reason cast iron was used for machining equipment.)
