If you want to purchase variety of Japanese Gravure-Idol movies with high quality by downloading, there is practically one choice.
In this area, DMM.com keeps a monopoly.
The site is also suitable for downloading Japanese films including adults films, Japanese animes, and fanbooks.
Check the “Gravure Idol” page yourself. Unfortunately, unless you are a member, you cannot watch trailers.
The company announces that movies can be downloaded only inside Japan. It is very unfortunate.