This page has the Japan Oricon chart positions:
http://park10.wakwak.com/~techno/japan.htmlNon-Japanese artists rarely made it into the top 20 of that chart, and even acts like YMO, who were huge didn't have many hit singles. It is mostly j-pop or idol singers that had the really big hits (Seiko Matsuda, Hiromi Go, Kenji Sawada, Pink Lady etc).
Japan were a big act in Japan - in terms of media they appeared in all the major magazines, even titles that didn't usually feature western artists due to later interviews with YMO members; they also sold out the biggest concert venues of the time and have left behind a back catalogue that has been re-issued and repackaged even more than it has been in the UK.
Mick Karn managed the biggest Oricon chart hit of a Japan member with NiNa, a Christmas No1 no less. Steve Jansen had the next biggest hit with "Stay Close" - in both cases they were in partnership with established Japanese artists and did ample promotion. Steve claimed in an interview that Stay Close was No1 for 8 weeks but I'm not sure which chart that was...
Steve won't have lied as there are other charts in Japan, such as the Music Life chart of non-Japanese acts, and the Tokyo Hot 100, airplay based, which Sylvian/Sakamoto charted very highly on with "World Citizen".