Many parishes starting using Parce Domine in recent years, partly because it is a remnant of chant that oddly survived in antiphon form within modern missalettes and hymnals in the Catholic world of today. But where are the verses? You almost wouldn't know that it had any, until the Parish Book of Chant.
Richard Rice put them together in a single file so that it can be sung with the congregation on the antiphon and the schola or soloist singing the verses. Here is the file for printing.