Nti Ngơi Nau Bu Nong (Central Mnong Language Lessons) is a quaint booklet that came to us from one of my evening students who arrived in the US with her husband and family from Vietnam via Cambodia in 1992. It was pretty worn and had penciled notations. Another student also said she had kept her copy from the refugee camp, too.
From the Summer Institute of Linguistics (see http://www.sil.org/). Originally published in 1974 and republished in 1978.
There is a good brief overview in Vietnamese and English and an interesting list of Summer publications at the end of the booklet.
Mnong or Bu Nong (or Bunong)? All the speakers in our classes referred to themselves as Bunong.
Click on center button (by "Slide 01") to enlarge the slide show.