I wonder if anyone in Japan can call Mr. Nagaoka-san and ask if they would be willing to sell an 8x10 metal parts kit? Alternatively, if I could find the phone number I could ask someone from my Japan office to call him (I understand he doesn't speak English).

If he (or his supplier) is willing to sell parts kits for the various models that might be a lucrative sideline, and at least keep demand high enough so that his suppliers can keep making parts.

Apparently you can still buy the complete cameras, with a basic 4x5 going for about $750: http://www.ohban4x5.com/nagaoka.html