I knew there had to be at least one more amazon site... :)
I tried to find a way to contact you outside of the WP forum to continue discussion there instead of cluttering the thread, but no joy.
Ok, I have had a very quick look at the amazon.jp site and the initial diagnosis is not good. The main problem is that many Japanese-only items don't list on the .co.uk or .com databases (I think the japanese venture is a separate beast). This wouldn't be too much of a hassle if I actually spoke Japanese, but I do not.
This sadly makes parsing the unicode in the amazon.co.jp links impossible for me, so I am unable to make the system extract the item data.
However, there is light at the end of said tunnel...
What I *can* do for you is modify the system to use the .co.jp extension, and to generate .co.jp associate links and, even, extract the items image. You will then have to manually enter the item title, author and type. (As extracting them from the hopeless mess that is the amazon.co.jp website is mission:Impossible for an english speaker such as myself.)
If this would help, let me know and I'll adjust the code for you.