I'm a wargamer based in Tokyo for the last six or seven years, and I can confirm there's not much of a tabletop gaming scene here, for all the reasons that jimbibbly mentioned. And I've never once seen a Japanese historical/samurai wargame played here.
I do know some clubs around Tokyo where they play GW games, Warmachine/Hordes, Infinity, Malifaux, etc. These clubs usually rent a room and set up tables at local community centers to play on the weekend. Living space is at a premium here, and most people don't have room to game at home. There's also not really a culture of casually inviting your friends around to your house; people tend to entertain outside the house (at bars or restaurants or whatever).
But on the bright side, geek culture is pretty widespread here and non-gamers are mostly very accepting of modeling/gaming as a hobby, even for grown men who should have put aside childish pursuits years ago.
Back OT, this looks to be another lovely build, jimbib! I've been eyeing off all your J-scenery for a dream project which I'll start one day when i have more room.