There is very little in English. This site is for Tokyo area primarily (haven't looked recently, might be more than Tokyo area now), in Japanese of course.
http://www.soap-japan.com/home.htm
This site has a few cities it serves.
http://www.mxy.jp/
There are many other sites as well. At least you can see price ranges and how much a yen goes for. Best time is afternoon, cheapest time, but selection is smaller, but since not busy, might let you in.
Depends where you are going to be, though every Japanese city has soapland or associated type bars/clubs/massage/spa/whatever they call it this month to avoid police. Non-Japanese are not readily accepted, expect to be denied 75% of the time, even more if you can't speak Japanese. If you are with Japanese salaryman, might improve odds to around 50%.
Best solution is to meet lady in a bar, married ones are quite good and playful for foreigners. Also just walking around train station, pick almost any, within a block is soapland area 95% of the time. Then look at photos, if doorman doesn't shoo you away and you like girl's photo, then try going in. Often you will be offered foreign ladies instead of Japanese. Just ask for nihon-jin and they will say ok or show you the door.
