The Choral Domain Public Library has a page with links to a couple of different versions of the score. We will be working from the more recent one, by James Gibb. The accompanying MIDI file seems to be pretty good, though the tenor part seems to be missing in some places. The CPDL files can be freely copied and redistributed.
Bill Gaudie drew my attention to a very good performance on Youtube (performed in 1994 by Choeur de Chambre de Namur, La petite Bande, Sigiswald Kuijken). I make no guarantees that this video is unencumbered by copyright: if you get extradited to the USA with Kim Dotcom, don’t blame me.