You find materials on medieval saints in the following libraries.
Classics Library Collection--for early Christian saints
Literatures and Languages Library--for saints lives
History, Philosophy and Newspaper Library--for historical and religious aspects of sainthood
Music and Performing Arts Library--for saints in music
Ricker Architecture and Art Library--for the visual tradition of saints
Christian saints - Biography - Dictionaries
Christian art and symbolism
History, Ancient - Historiography
The general databases listed under Starting Research are an excellent place to start for materials on medieval saints. For saints' biographies and hagiography, consult the literature databases listed here.
For historical context, consult the history and religious studies databases.