Hi Michael,
Well, every library should certainly have a copy of Ian's Arms and Armour of the Samurai which provides a great overview of the subject. If you're looking for scientific analysis or an academic approach to the study of armour that is more technical and specific, from the list of books presented at the link, then I would recommend Robert Burawoy's Armuriers du Japon: Etudes de Meiko Zukan (if you speak French of course). Trevor Absolon's Samurai Armour: The Japanese Cuirass is a hefty tome that goes into great technical (and at times, historical) detail about the dō. The first three yearbooks of the JAS have presented some very in-depth (and frankly, cutting edge - pun intended) articles on subjects as varied as toppai, momonari and Joshu kabuto, the Japanese matchlock, and the Nobuie controversy, presented by the most senior experts of the society in Japan, as well as Western scholars such as Robert Burawoy. As well, membership in the JAS provides partial translations of the society meetings, some of which have presented very serious discussion on varied topics relating to katchu. Hope this helps!