Take pictures and post them here. That plastic part is not what you are looking for.....the nipple turning out of the wall whether copper or brass should be 1/2" IPS and most if not all replacements will work.
They made a tub spout years ago that weighed a few pounds and had a specific thread at the wall that was hard to find, fine threaded as well. I'm glad I work with homes that are normally no older than 30 years old.
The real old homes where the customer wants a rebuld/repair over replacement have you running to supply houses constantly.