Osprey has tons of books on the subject.

http://www.ospreypublishing.com/eastern_warfare/

If I recall correctly Steven Turnbull is the expert.

http://stephenturnbull.com/

And for movies, Ran was the start of it all (Shogun Total War), and see more on this page:

http://www.amazon.com/s/ref=nb_sb_no...d-keywords=RAN