You can also browse and buy from DMM (if you understand japanese).
http://www.dmm.co.jp/digital/videoa/-/list/=/article=keyword/id=4015/sort=release_date/
If you leave abroad, they now accept foreign credit cards since last year.
On Ririca twitter (which is now disabled) :
http://webcache.googleusercontent.com/search?q=cache:fNAPy5magDMJ:https://twitter.com/Ririca777+&cd=1&hl=fr&ct=clnk&gl=jp
And on the blog of a friend of her (Itsuki) who works for allure helthclub in fukuoka...