Reddit reviews Schoolgirls, Money and Rebellion in Japan (Nissan Institute/Routledge Japanese Studies)

Is this for high school or university?

Anyway, you're unlikely to find anything about the recent law from an academic source - especially one in English. Amazon has a few sources (here's one) that might be relevant, but you have to be vigilant about checking the credentials of the authors. Plus if you buy a lot of them it's going to be quite expensive. Your library might have an inter-library loan program where you can get additional sources.

Have you thought about charting regulation through history? There are many, many sources on prostitution in Japan, especially concerning WWII and anything pre-Meiji. It will help you get your source count up and more importantly, give you a better understanding of the context of where these regulations come from.

My other favorite paper trick is to look at similar situations happening elsewhere. Did someone else pass a similar possession law sometime in recent history? What were the effects of that law. You have to make the conceit in your paper that the situations are not equal (so if the UK passed the law, you have to concede that Japan and the UK have vastly different cultural identities), but it might help you get an idea of what the global perception is about these types of things.

Hope that helps. Good luck on your project.