do a search on amazon for 'medieval weapons'.
do a search on amazon for 'medieval history'
I'm researching for a novel at the moment in this era, and have so far got hold of numerous books from amazon on horsemanship, archery, a medieval military dictionary, castle life and construction, rural economies, medieval warfare from the english perspective, a book on the economics of warfare in that time, as well as an account of the wars of the roses and the crusades, i also picked up some stuff on caesar's 10th legion and a book on tactics.
it costs a bit of dosh, but failing that, you might find some decent stuff on
www.questia.com which costs about £8 a month to join, but gives you access to various texts. i know it has some history stuff, journals etc. but you ought to do a search to be sure.
try
www.abebooks.com for the titles you see on amazon, as abebooks is all second hand stuff, try your luck with that.