As far as JP server's with Oceanic communities go you've got-

JP Legacy - Masamune
JP New - Tonberry
JP New - Tiamat

I'd assume there are also people spread about on other servers but those are your most likely picks, as far as I'm concerned however if you want a large picking of the Oceanic player-base Tonberry is where it's at (biased) there are many and more Free Companies there sporting varying time zones and large amounts of activity.

Hope that helps.