As I understand it Miyata made and exported high quality, Japanese made frames until the value of the yen made that unprofitable. They then folded up shop in the USA around the mid-nineties. Koga-Miyata is a Dutch/Japanese venture, Koga being the Dutch part. It looks like most of their bikes are now built in Taiwan/China.
Those old splined tubing, triple butted, lugged, steel frames are a thing of the past it looks like, though they still make some lugged steel road frames. The glued carbon, titanium and aluminum ones that you mentioned (and that I love too) are no longer made.
Check out this older carbon one though:
https://www.dli.ch/Hobbies/Bikes/Travelbike/#general%20Information
I'm still trying to figure this crank out that's on it:
https://www.dli.ch/Hobbies/Bikes/Travelbike/MVC-236F.JPG
https://www.koga.com/
https://www.kogausa.com/