That's a great question. I tried looking for it this past week in the Triplex and the modern Antiphonale Monasticum and couldn't find it. My choir rendered Hanson's SSATB a capella setting of it yesterday, preceded by the chant. It was very nice. If you can find where it's located, I'd be interested in knowing, too.
Even in the AO (EF), O vos omnes was a repons not in Antiphonale monasticum neither Graduale. It is a matutine-piece, and i think not that it has been removed from in OF (NO). See ad Vigilias/matutines on holy saturday...
To participate in the discussions on Catholic church music, sign in or register as a forum member, The forum is a project of the Church Music Association of America.