While searching for a version of Corelli’s ‘Christmas’ Concerto arranged for 20 cellos (don’t ask !) I came across what looks like a very useful website. Basically it is source of editable sheet music and includes a vast array of classical music.
… and yes, as you can see, I DID find what I was looking for. I could download it free if I paid an annual subscription.
Play String Quartets ! 