Depends on the kind of music you're looking for.... most of the japanese mp3s I've found wouldn't be too conductive for meditation.
C'mon...you really gonna meditate to "kinki kids" or "bump of chicken" (yep, those are real bands). If you're looking for lively japanese music, do a search for CDTV. also...hard to find if you don`t have a japanese viewer.
For more traditional kodo, koto, flute music, in most large CD stores in america there are international sections. Look under the listing for Japan and you should find a lot of tradional