So far, I'm applying to these schools:
The Naganuma School a.k.a. The Tokyo School of the Japanese Language (deadline is Sept 30, which there's no way I'll meet, but apparently they have a "secondary offering" in October. Whatever that means. In other words, it may already be too late, since they require you to apply through someone in Japan, and you can't apply directly. But I'll give it a shot anyway).
Keio University's Japanese Language Program (deadline is October 10th).
Waseda University's Intensive Japanese Language Program (deadline is October 14th).
Sophia University's Japanese Language Intensive Program (deadline is November 17th. I think. I'm not quite sure about this, the information I've gotten so far isn't entirely clear).
(I like how they all manage to have different acronyms for their programs.)
At any rate, I would imagine all of these are hard to get into -- what I really need to find at this point are a couple of outlet schools, so I need to find a couple more schools to apply to (I suppose there's always Sapporo). In the meantime, I'm scrambling to get materials together -- it's like applying to college all over again!