Aha!
Okshon.
http://www.okshon.com/
They're sort of a English-language brokers to Yahoo Japan Auctions. They've got a primitive machine-translation, which gives strange results sometimes, but I think you can contact them to get a proper translation (for a fee). Alternatively there are a few Japanese-speaking people here on KB who might help you out if you ask nicely.
Okshon does have a small fee, but it's more than worth it in savings.
EDIT: I believe the Suzuki Bandit 250 shares the same motor (different cams and carbs, I would think) with your bike. If you had the GSXR400, then not only is it the same as the Bandit 400, but the RF400 as well. So there's another option at least.
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