I was looking for Japanese government records on international marriages in Japan. The Geography major in me is continually fascinated by this sort of thing.

Min. of Health & Welfare nationwide figures for 2000
Total marriages: 798,138, of which:
Japanese husband-Foreign wife: 28,326
Foreign husband-Japanese wife: 7,937
total mixed marriages: 36,263 or 4.5% percent
Origin of non-Japanese spouses:
Foreign-born wife:
China 34.9%
Philippines 26.5
Korea 21.9%
Thai 7.5%
Brazil 1.3%
USA 0.7%
Other 7.1%
Foreign-born husband:
Korea 31.6%
USA 18.7%
China11.1%
Brazil 3.5%
UK 3.1%
Other 32%

So the big numbers once you dip into the data, this excel spreadsheet lists partners by nationality, show that there are big changes afoot.
In 1980, only 1% of all Japanese marriages were international. In 2002, 4.7%.
The biggest increase, surprisingly, is with Japanese men marrying non-Japanese women: from 4,386 back in 1980 to 27,927 in 2002. The majority of these marriages are with women from China (10,750 in 2002), the Philippines (7,630), and Korea (5,353), and Thailand (1,536). Only 163 of marriages in 2002 of Japanese men were with Americans.
For Japanese women, there are much fewer international marriages, 7,922 in 2002. Of these 2379 to Koreans, 1488 to Americans (19%), 814 to Chinese, 104 to Filipinos, and 45 to Thai men.
Someone who went through the data before me noted that this data may be skewed by the significant Japanese-born Korean population.