There are collections of festival books in many of the world's great libraries. These are the most important, after the British Library.
National Art Library in the Victoria and Albert Museum (London): Piot Collection of over 500 festival books
University of London. More than 100 of their festival books have been now digitised and are available online as pdf (Adobe Acrobat) files.
Rondel Collection in the Bibliothèque de l’Arsenal (Paris)
Bibliothèque National de France (Paris)
Bayerische Staatsbibliothek, (Munich)
August Bibliothek (Wolfenbüttel): the Federal German Library
with responsibility for 17th-century German imprints. You can read
314 online here.
Staatliche Kunstsammlungen (Dresden)
Getty Research Institute in the History of Art and the Humanities (the Lafranchi collection), California
New York Public Library (Spencer Collection)