I think it will be difficult to find a genuine Winchester lever outside of the used market. There might be some repops out there but I would think they're likely cheap castings that need work to fit properly. You might try Gun Parts Corporation but that's just a maybe. They may even carry repops.
The only other suggestion is see whether Taylor's and Company can help. I bought one of their 1892 Rio Bravo carbines that are a modern clone...maybe the parts might be interchangeable if available.