Older resources:

Fact sheets and articles about the complex workings of Japan’s crime organizations.

Yakuza Studying Up On How To Circumvent New Anti-Organized Crime Laws October 2008

A listing of Japan’s Twenty-Two Officially Designated Organized Crime Groups, from the National Police Agency White Paper 2008.

You’ll notice that even the yakuza office locations are clearly designated. They aren’t a hidden and secret society.