Alibaba lists over 300 manufacturers and suppliers of bicycle inner tubes in China, alone. Manta lists 96.
I know there are several in Thailand and Vietnam. The last I knew there were two still companies cranking out tubes for bikes in the U.S.A., but I don't know if the plants are still in operation. Akron, Ohio...sadly...has not been the rubber capital of the world for several decades. The last thing of note to come out of Akron was the rock group, DEVO. Yeah, whip it good.
Hutchinson still makes their own tubes in France, but I have only used their sew-ups. Never their clincher tire inner tubes.
I have a few Giant tubes ready to go into the rotation. I've never used them and have no clue 'who' makes them. In the Global Economy™ it's getting more difficult to find the real source of any product inside any box marked Hecho en Chine!