The Tokyopop site use to be much easier to get around until they revamped it into the current version. I managed to locate the novels before the site went down but don't remember what dates they had listed.

Okay, went back to the site and the suppose release date for book four is today. Here's the link. http://tokyopop.com/shop/1448/ScrappedPrincess/4.html There's no mention about five and until the volume five becomes black, there won't be any info.