Call the Big Siemens generator and gas turbine manufactoring facility in Charlotte.
They handle that big of casting, forgings, and machined surfaces regularly, with accuracies much higher and tolerances much lower all the time.
The machining consumables, and specialized tooling (lathes, mills, CNC) and cranes and trained labor will come with a larger "overhead" price for a big company like Siemens than a smaller mom-and-pop machine shop with only a forklift for a crane, but then again, you are not looking at a small part. Also, you may face a conflict with emergent Siemens repair work and "in-shop" priorities for the big lathes on the production line for generators or GT's, but if you are a paying client, then the facility manager needs to fit you to his schedule according to your contract.