The Toronto Mendelssohn Choir Library maintains an extensive choral library of over 70,000 volumes, including many out-of-print works.  Scores are available for rent, twelve months of the year, at reasonable rates.  The TMC has recently updated its catalogue.  Check it out online at http://www.tmchoir.org/about/choralMusicCatalogue.cfm where you can download a PDF of the full catalogue.