Took a look at Wikipedia. There have been 55 Japanese players who had major-league debuts, since 1964. (There was one in 1964, and then no more until 1995.)
Of the 55, 17, or 30.9%, signed with one of six West Coast clubs: Six each with the Dodgers and the Mariners, two with the Giants, and one each with the Athletics, Angels and Padres.
Northeastern/mid-Atlantic clubs (Red Sox, Yankees, Mets, Orioles) collectively signed the same number of these players - 17 (eight by the Mets, four each by the Sox and Yankees, one by the Orioles. If we also define the Braves and Rays as "East Coast," then six East Coast clubs collectively have signed more Japanese players than the six West Coast clubs.
The club that has signed the most is the Mets, with eight. A total of 22 different clubs signed Japanese players who appeared in the majors. (The Phillies are not among the 22.)
The other ten clubs? Three (Rangers, Cubs, Indians) that signed three players; three (Brewers, White Sox, Twins) that signed two; and four (Royals, Cardinals, Pirates, Tigers) who signed one.
So... 19 players (34.5%) signed by East Coast teams; 19 players (34.5%) signed by middle-American teams; 17 players (30.9%) signed by West Coast teams.