The 60s films are the main ones to research, but gems may be anywhere.
From some of the very few reviews by users and critics, and looking at some associated stills, we can be sure that there is first-rate noir cinematography present in some of these films.
This is a gold mine waiting for re-releases with English subtitles.
As an example of this man's work with Fukasaku, see https://archive.org/details/HakuchuNoBuraikan1961
The film can be downloaded or viewed but it has no subtitles. The source has one review and IMDb has another, both calling it noir. Both the IMDb reviews are dated 2001.
From what I've seen, there is real and relatively undiscovered/unheralded noir here, much as in Greek cinema and, to a lesser extent, some other countries like Yugoslavia, Poland, Hungary and Czechoslovakia.