I worked for Apple for many years, and I spent a lot of time in China. I have to say, there’s nothing quite as exciting as running around a factory trying to get something to happen where no one speaks any English, and no one knows where the screwdrivers are. The engineering problems that need solving are usually tangible and immediate, and with pigeon Mandarin and a sketchbook you can accomplish just about anything.
Of course there are big watch factories in China, however it never occurred to me to visit them. It would have been so easy! The Seagull Watch Group has been around since 1955, and operates a huge factory in Tianjin, just outside Beijing. The Seagull Watch Group manufactures literally every kind of watch movement under the sun. As an example, here is a bare tourbillon movement (ST80 Series > 8007).

I’ve inquired about costs and minimum purchase orders. Hopefully they’re friendly!