The National Library of the Netherlands (Koninklijke Bibliotheek) offers an excellent online resource for the study of medieval manuscript illumination. Manuscripts of particular interest to students of arms and armor include:
Livy, Histoire Romaine Paris; c. 1380-1390
The Hague, KB, 71 A 16
Vincent of Beauvais, Le Miroir Historial (Vol. IV) Paris, Master of the Cité des Dames (illuminator); c. 1400- 1410
The Hague, KB, 72 A 24
Jean Froissart, Chroniques (Vol. 1) Paris, Virgil Master (illuminator); c. 1400-1410
The Hague, KB, 72 A 25
The link above will take you to a search page, and you can enter the shelfmark, which follows "KB" above, to reach the particular manuscript."Images and Text" will then give you both thumbnail images from the MS and text describing their context.