I'm not sure he has a 'shop' as such where you could walk in - from what I understand, he's running the operation online / via mail. But you could always contact him and ask

He's very reliable - I've sold a few of my basses through him, and his s service has always been excellent.
In terms of places to visit, there are mainly 3 spots I'd recommend:
- Ochanomizu: many big stores here, including Guitar/Bass planet, The ESP/Boss store, Ishibashi, Shimamura (or Shimokura? I forge which one is where), etc.
- Shibuya: Ikebe bass collection & Grandey's Bass (BC does the 'high end' stuff, Grandey's is the more usual stuff), Kurosawa Gaggki G-Club, Key Music, and I think there's also an Ishibashi in there somehwere,
- Okubo/Shin-okubo area: Kurosawa 'Bass Center', Barchie's Music, and TC Gakki
There are also some other instrument shops at other major stations (e.g. Ikebukuro has an Ishibashi & Ikebe Rock House, and Shinjuku has couple too), but if you want to visit the most bass/guitar focused places, then the above thee areas/stations should keep you busy for a few days.
Enjoy the visit!