A friend of mine contacted me looking for the sheet music for Iesu rex admirabilis, the version found in the beginning of sound of music from this link https://www.youtube.com/watch?v=6w9Jbi3xgr8 (at around 1:45)

I am very unfamiliar with this version--we always use the Palestrina. Does anyone have an idea of where I could get this? He says that it wasnt something composed by the movie, but a real polyphonic that existed before, but I really dont know anything to help him.

Thanks.