You're only allowed 3 foreign players in Japan anyway.
I know a couple of useful Japanese players:
Yunichi Inamoto (DMC, 24, Fulham)
Yoshikatsu Kawaguchi (GK, 28, FC Nordsjælland)
and some talents:
Yutaro Miyamoto (ML, 16, Jubilo)
Kanto Sugawara (MC, 16, Vegalta)
Kento Tsurumaki (MRC, 16, Verdy)
Shota Nakadai (SC, 16, Reysol)
Havenaar Mike (or Mike Havenaar, SC, 16, F MARINOS (that's you ))
I think most Japanese youth players would have random potential, though. (:/)
And you could try getting Fredy William Thompson as one of your foreign players, of course...