I've had the long on-and-off trying to get more info on KHS due to their slavish cloning of Conn 1960s designs, before they branched out to other designs. While this channel seems to cover Japanese makes primarily, from what I can tell, it's quite a lot to take in [I can't tell what any of it says without translation help] and he's not even sure about Nikkan serials, for instance...https://www.youtube.com/@olds3/videos
I guess it's reassuring he's had similar issues finding info on some of the smaller firms, due to the usual lack of surviving documentation and such...?
Books
Horns of Uncertain Pedigree Topics
and various Japanese brasses Posts
https://kuwahata-shouten.com/ was linked in one of his videos, and it appears quite interesting as well
[so is http://www.mp-museum.com/ for the record]
[so is http://www.mp-museum.com/ for the record]
https://kuwahata-shouten.com/2024/10/15/%e7%94%b0%e8%be%ba%e6%a5%bd%e5%99%a8%e3%81%ab%e3%81%a4%e3%81%84%e3%81%a6/ - Tanabe history [seems part of it became part of Kawai] / https://kuwahata-shouten.com/2024/11/01/%e5%a4%a7%e6%ad%a3%e6%9c%9f%e3%80%80%e3%83%88%e3%83%a9%e3%83%b3%e3%83%9a%e3%83%83%e3%83%88%e3%80%80%e6%97%a5%e6%9c%ac%e7%ae%a1%e6%a5%bd%e5%99%a8%e8%a3%bd/ - the "fake import" is rather interesting