One of the big problems you often run into restoring a classic watch is that the crown is shot to pieces. I posted on the watchmaking side about Acon Watch Crown, the only manufacturer of watch crowns in the USA, but I thought this might be a good place to expand a bit on it.
they have a broad range of every possible crown that will fit the watches of just about every era. In addition, they're a useful source for pocket watch crowns. they also manufacture watch buckles too.
While Im at it, I might also mention Perfit crystal in New York City, which is the only manufacturer I know of in the USA still capable of making glass crystals for wrist watches. I don't mean mineral glass or sapphire glass, but honest to goodness glass crystals, which were still in use into the 1950s on many watches.