Nippon Radio Corp? ........Now Japan Radio Corp? (Not to be confused with New Japan Radio Corp, maker of chips and stuff.)
Their 1930 history is interesting:
http://www.jrc.co.jp/eng/company/html/history.html
and in 1942, they changed the name to Japan Radio Corp, (Nippon Radio Corp)
https://en.wikipedia.org/wiki/Nippon_(disambiguation)
...that's my guess.
This Japanese Ham/Homebrew extraordinaire is one place I'd start - he used to show up in some old Usenet electronics forums with help finding information of Japanese parts and radios:
http://www.intio.or.jp/jf10zl/
Cheers,