I just googled the probable original Japanese titles of the first four listed seized items. I found they are all available on Amazon.co.jp (3 available as used from third-party vendors, 1 as new directly from Amazon). From the covers it's clear these are the items in question.

It's not like you need to go underground to buy them; Amazon is selling them, though obviously Japanese standards of what counts as obscene are different than those of the U.S.