A good series is Marshall Cavendish W.W.I series. This 12 volume set, is usually found in libraries, encyclopedia articles of the war, some written or based on people who lived during the war.
Rich in pictures, graphs, charts, illustrations, side stories of the Great War. If you cannot find what you want to read here, then it probably be a hard search for that particular subject.
Some libraries hace a duplicate set of books, letting you take a volume home. You can try the net, used book stores, good luck in getting a set, enjoy the read, thanks, Pellulo