Like I stated above, the Loaded models and below at SAI are made by Imbel in Brazil. SAI makes the slides, barrels and most of their small parts themselves, on all their 1911's.
On the Range Officer, TRP, Professional, etc., SAI makes the FRAMES as well as the rest of the pistol.
I can only think of 1 company in the world that currently is making 100% of all the parts on their handguns and that is Sphinx in Switzerland. Everyone else outsources numerous parts.
Ed Brown makes all of their parts in house. They aren't within range of the OPs post but saying there is only one in the world is inaccurate.