I think I’ve found the correct camp. According to this website, Hakodate Camp 2-B changed its name first to Tokyo-6, then Sendai-4 (Ohashi). Which means two things, first, that I’ve been looking in the wrong places, and second, that this afternoon I held the file for this very camp in my hand and passed over it. In the speech below I’ve bolded some of the text about Ohashi.
Another trip back to the archives. According to this page:
the information is located in box 2131, RG 389 at the National Archives.
Another one I need to check out is a report of supply missions flown to the POW camps right after the war, when supplies were airdropped from bombers. The report is in Record Group 243, Entry 53, Stack Area 190, Row 63, Compartment 29, Shelf 2, Box 9 — I’ll get it and scan it and post it.
I’m going to link to the page here: