https://www.recoilweb.com/review-springfield-armory-sa-35-the-modern-browning-hi-power-171049.html
"Springfield Armory didn’t just take old machine drawings and plug them into a CNC. They started with the blueprints as a rough guideline to bring the Browning Hi-Power to modern times. We’ve made an advance or two in metallurgy in the last century, and Springfield Armory certainly took full advantage. Just as with their 1911s, Springfield starts with raw forgings for SA-35 slides and frames to maximize strength and durability. Then, the slides, frames, barrels, as well as nearly all the small parts and pieces are precision CNC’d and then heat-treated with present-day methods."
The above is an excerpt from Recoilweb.com. Theoretically, the forged blanks could be coming from anywhere or even multiple sources of supply. Often, the actual provider(s) is/are proprietary. This apparently was different from the "Imbel" days of Springfield as those particular frames were probably completed in Brazil back then, causing the frames to be marked made in Brazil. Perhaps more than just the frames were completed in Brazil back then. Maybe, someday, we'll get a Springfield-Armory photo of metal being removed by a CNC machine located in Geneseo IL, of an SA-35. It would likely help Springfield-Armory (if true). I suppose unless someone has a picture of a crate/box/pallet/shipping container coming in from Turkey, arriving at Springfield-Armory, we'll never get much "proof".
For example, here's one company I'd never heard of which merely provides forgings and is located in the same state as Springfield-Armory:
https://www.anchorharvey.com/industries/
But really, in company in the world could be providing raw forgings to Springfield and depending on competition, demand, sourcing, Springfield could have set up two or more companies if that makes sense from a procurement standpoint. Other times, it could make sense to go with only one source for better pricing and these sources could be overseas.
Here's another source:
https://presrite.com/contact-us/