yes I have bought a few things from there, but never directly. AFAIK, Mak Japan will not ship to anywhere outside of the country.
basically the only ways to buy from them:
a) go down to Akihabara yourself and visit the shop in person
-or- while you're in Japan, place an order thru E-mail/fax/telephone
b) bother someone who is in Japan to purchase for you, then have the item delivered overseas
from what I hear, the language barrier shouldn't be a problem if you go there - just pick up your item(s) and pay at the counter. they'll even offer to test out any PCB you buy right in the store.
prices for their stock are decent on the more common games that you can find elsewhere, and they will make custom PCB harness/JAMMA adaptors on request, though I think other shops do this as well.
p.s. I like
Game Kanaya and G-Front better. higher prices, but they usually have a good selection of rare games.