Visit CS Hirose if you can!
Hirose site (in Japanese)

Also, anyplace that sells TOEI frames. I think you can't visit the Toei factory unless you are like friends with them.

In my googling, the Tokyo Cycling Club forum pops up sometimes. Maybe go on there and introduce yourself? They seem to be an ok crowd especially for non-Japanese outsiders.

Nitto products are pretty available and affordable over here, as are Panaracer tires. These to me represent the best in their field. But are Honjo fenders maybe cheaper over there? Honjo fenders seem overpriced in the states, so maybe it's a case of a captive import market like Peter White has been doing jacking the prices up on Busch and Muller stuff, which you can often get in Germany for half what he sells them for here in the USA.