I use amazon japan for all my Transformers needs, and toysapiens for imported stuff.
I know toysapiens is the "official" distributor of Hot Toys in Japan but I've seen lower prices on amazon so just keep an eye on what you're looking for on both sites.
Amazon has superior service obviously, but toysapiens wasn't bad...just if they run out of stock and your item is damaged, returns are more of a pain. I've used toysapiens for Star Wars Black stuff and they were really good. They'll also sometimes get really limited SDCC exclusives so that's another plus. Drawback is they're not always cheap.
I'm in Saitama btw, not Okinawa, but I'm sure these websites are your best bet and of course like the others said, if you can come to Tokyo, you'll go nuts in Akiba and Nakano....it's insane!!