Where can you learn zangan-ryu?

Hiten-Mitsurugi-Ryu is a fictional martial art, so it can't be learned.

In California, your only alternative is Kendo. Or if you're traveling to Japan there are schools in Kenjutsu which was banned during the occupation of Japan post-WWII but have reemerged in recent years. Kenjutsu uses no armor during training and uses wooden sWords for practice that are as capable of killing a person as a real sWord if mishandled. This is the style taught to Samurai in Japan for hundreds of years. There are different techniques and varying styles of Kenjutsu, but they are all rooted in basic principles.