John Deere - if it actually says John Deere, they make it themselves. If it is "Frontier", then it is made by someone else, and they use dozens of contractors. You can find out who made which item by reading their spec sheets or by checking the warranty page of the owner's manual.
I think that Kioti gets some of their stuff from Midwest; not sure which items or if it's everything with their name.
I have a John Deere 660 tiller made in Germany by Howard. Even has Howard stamped on the tines. I know John Deere is going to Chinese made gearboxes in some of their equipment. I know, of course, that the Chinese can and could make gearboxes second to none. That said, its been my experiance when a company goes to China to cut a few bucks off the cost of making a product quality usually suffers.
A Kubota tiller at my local dealer had a big "MADE IN ITALY" sticker on it. Looked high quality. LOVED the paint job.......
Clarify your request, please...
If you're asking who manufactures implements that are rebadged or proprietory for those manufacturers...that's one thing.
If you asking who manufactures implements that fit those tractors...that's another thing altogether.
I’d bet a bunch of companies make different things for the big boys. I know for sure that a friend in the metal business made bale spears for Kubota as well as varies parts for their backhoes. He was also making parts for John Deere last time I was at his shop.