U.S. foundries to manufacture castings? I don't know of any though here in Canada, I would bet the Lunenburg Foundry could do it.
I worked there as charge hand carpenter in the late 1980's when they made the Atlantic make-and-break engines as custom orders.......maybe they still do!
Here's a link to the foundry site
http://www.lunenburgfoundry.com/ and here is a youtube link showing an 8Hp twin
https://www.youtube.com/watch?v=Mg8W6gYTXR4When I worked there there was a blind machinist (yes, blind) who did all the machine work on the Atlantic castings, then assemble the engines. He could tell a drill size by feel and read a micrometer with his fingers. The pattern storage area up in the attic of this place was incredible, they never threw anything away.
The actual foundry was a throwback to the turn of the century (1900) operation. Not much different from the Rajkot operations we see today, but the foundrymen wore boots and leather aprons. After a pour, the foundry floor was like a vision of walking through hell......dark and smoking with glowing molten metal. I was privileged to be present at several pours, wish I had filmed it.......an amazing and dangerous process in which each man has his particular part to play. When the clay plug was smashed and the iron began to flow, there was a careful rhythm to the pours. After one run through with all the ladles being carried to and emptied into the molds, the stopper would jam another clay plug into the retort outlet, everyone drank a dipper of water from a barrel. Then line reformed, the plug was smashed and the pour continued.......what a show!
This is a family run business and has been for more than 100 years. It would be surprising if they could not make good castings to replicate a Lister.
Can they do it in a financially viable way? You'd have to ask.
Cheers,
Hugh