For those who wish to buy these books/CDs/DVDs directly from Japan, here is some information. Please note I've never dealt with them personally and please use the information at your own risk.

Amazon is an obvious place to try. They have a branch in Japan and should be able to get most of the things (books, CDs and DVDs).

You can also try Book Services.
This relatively new on-line shop is a subsidary of Yamato Transport (do you know Kiki's Delivery Service?). When I asked, they said they take orders in English but, as they have no one fluent in English in the staff, please send orders/inquiries in plain easy English. They seem to ship CDs and DVDs as well as books.