The word repertoire, with its other variant repertory, did once have the meaning of an inventory. Etymonline explains:
1550s, "an index, list, catalogue," from Late Latin repertorium "inventory, list," from Latin repertus, past participle of reperire "to find, get, invent," from re-, here perhaps an intensive prefix, + parire, archaic form of paerere "produce, bring forth" (from PIE root *pere- (1) "to produce, procure").
So there is a connotation of all the items of a collection, which was preserved in the specific meaning with which it is used today (performances).
For libraries, however, if you want to refer to the amount itself, better use collection
an accumulation of objects gathered for study, comparison, or exhibition or as a hobby (M-W)
In fact, library is listed as the synonym of collection.
Here are some official examples:
The British Library’s collection includes books, journals, manuscripts, maps, stamps, music, patents, photographs, newspapers and sound. (source)
If you refer to the list that contains all the names of the book, catalogue (or catalog if you live in the US) is the best term.
a complete list of items, typically one in alphabetical or other systematic order. (OxfordL)