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):
http://mora.jp/package/43000001/4534530058010/
http://mora.jp/package/43000001/4560429780076/
http://mora.jp/package/43000002/ANTCD-3106/
http://mora.jp/package/43000014/KIZC-211/
http://mora.jp/package/43000014/NMAX-1153/

Albums @ Recochoku (examples):
http://recochoku.jp/album/30282664/
http://recochoku.jp/album/30284257/

Songs @ Recochoku (examples):
http://recochoku.jp/song/S21893898/
http://recochoku.jp/song/S20103490/

The trailing backslash is required.