I was at a militiria show this weekend and meet a older gent that has been liquidating his collection of Japanese gear. He knew his stuff and was buying all this gear when it was cheap from the early 70's onward. He had lots of rifles of every type, date and manufacture and lots of spare parts for Japanese firearms.
This was his first show in a long time and was selling off his gear before he passes away. In case you need something particular or just spare pins, springs and plates his email is firstname.lastname@example.org. He did state that he supplied the Fort.Bragg and Fort. Gordon museums with gear in the past.