At the Chabanel Psalms site, on the Accompaniments page (with NOH), there is a Polish Kyriale Accompaniment book. It includes the three most common Messes du Plainchant by DuMont, beginning on pg. 91 on the book (98 of the PDF scan).
This is thrilling news!! Salieri, thank you soooo much! I've been looking for several weeks now and was going to email Jeff Ostrowski next to see if he had any leads.
This is a very useful collection of music, by the way. It's always nice to have different accompaniments to the mass settings so things don't get boring. I'll definitely be using a number of things from this book.
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