As far as I know they do not have agency securitization as we do in the US. That is, no Ginnie Mae / Freddie Mac / etc as government sponsors of mortgage securitization. So mortgage pools trade as the "whole loan" market in the US.Again, as far as I know, this market is very illiquid in Japan. Edit: Or did you mean as a consumer, you're looking for a mortgage? Here is some mortgage rate data for a town in Missouri called Japan:
http://www.trulia.com/mortgages/Japan,MO/:) Seriously here is a relevant link:
http://japanpropertycentral.com/tag/japan-mortgages/