AEG has just released the Strongholds of the Empire, the first L5R only PDF sourcebook. The 4th Edition sourcebook covers a variety of places in Rokugan and how the clans run these strongholds. You can get the sourcebook at Drive-Thru RPG. The book is primarily meant to be bought as a PDF, but you can order a color or black and white hardcover book on demand from Drive-Thru RPG.
See more a l5r.com.