These are 2 major Japanese online stores - before Sony Japan caved in to iTunes Japan several months ago, these were the only big options. I don't know how to search Musicbrainz for URLs, but if there's a way, you can look at my edit history for these URL patterns and find them used by most of the major Japanese record companies.
I hope this doesn't need Style approval, or a magic number of already-added relationships. (I've been adding a lot but only starting recently. And it would speed things up if I no longer had to open the dropbox menu!)
Albums @ Mora (examples):
The trailing backslash is required.