The very first Gothic & Lolita Bible has much info on his store, so you may be able to find a translation to it somewhere. I do have also some maps on the area, so if you ever find yourself in Japan... ^_^*
Additionally, MTV in Japan has had at least two documentaries on his store (one while it was being built, the other while in use) so you might want to try digging those up.
Hmm...it'd be cool to actually buy something from MmM, but then again I'm not overly impressed with the originality of the design nor complexity in construction from what I've seen. Especially since we know Mana's so much more creative and weirder than that and most of his line can be easily reproduced. (Now, h. NAOTO and Black Peace Now seem much more interesting to me... ^_-)