Screenshot of Encore homepage. See link below.
If we need to borrow a set of orchestral or choral music, or if societies ask us to recommend a cheaper way than a commercial hire, then a good place to look is Encore.
Encore is a union catalogue of choral and orchestral sets in libraries. The precise loan arrangements can vary - some libraries will lend directly to choirs and orchestras for a fee, generally much less than a commercial hire. Others require the arrangements to be made between libraries, on behalf of their patrons.
Not all libraries do lend to one another, but if you find a piece of music on Encore, then it is generally available to be borrowed so long as it's not already in use at the time you want it.
It's good for standard repertoire. Obviously if something is only available through the publisher's hire library, then you won't find it cheap on Encore!