The numbers I mentioned yesterday were based on calories by the way. An article on the government report was published in The Japan Food Journal (Japanese) on 2008.07.18.
Some more interesting numbers from the same article are the following, concerning Japanese grain imports (how much and from where).
Wheat (148.9 billion yen)
America 53.8%, Canada 24.2%, Australia 21.9%
Soy (149.1 billion yen)
America 76.5%, Canada 9.2%, Brazil 8.1%, China 6.2%
Corn (300.8 billion yen)
America 96.3%, China 2.8%