Somewhere up in Northern New England there has to be some ancient family shop that's still quasi "in business" if you throw a bunch of money at them. The Clark family of Lincoln, New Hampshire has deep roots in the area and have always been interested in historic preservation. Look up Clark's trading post and give them a holler. I'm not sure if either Ed or Murry Clark are still alive. I worked for Ed on the Cog railway back in the 1970s.
My favorite Ed Clark comment: "Now take and listen to what I'm telling you. Whatever you're looking for, whatever you want, somewhere there's a room full of them and nobody's found them yet."
I'm still looking for my room full of Rivett 608s!
Another guy to contact would be Charlie Kennison. He has worked for the Cog railway as its general manager for a number of years. Not sure if he's still there, but he's an informed person and had a career as a foundrey manager in northern New England before going back to run Mount Washington.
The cog railway itself has a machine shop that used to be driven by line shafting, but like so many places, it's been upgraded slowly to circa 1935 though they may have made it to the postwar era in recent years...
The East Broad Top Railway in Pennsylvania has a good old machine shop I believe, as does the Edison Historic site in New Jersey. Someone has already mentioned the Knight Foundrey. Haven't been out in years, but that may be the oldest most complete.
Conrad Milster used to collect knowledge of industrial sites around the New York city area. He may still be at the Pratt Institute in Brooklyn where he presided over their engine house. No one else knew hidden New York better.
This is a great question.
I wonder if you couldn't contact some MSC reps around industrial areas and ask them the same question...although the type of place you're looking for would probably pride itself on keeping MSC orders down to an annual cost of something like$8.67
Has anyone taken the L.S. Starrett factory tour in recent years? Someone mentioned they have some older machines, and after all, it's still family run...