The only place I'd ever seen Belle Dorman Rugh's Crystal Mountain mentioned was as a fifth-grade reading choice in Diane Lopez's book Teaching Children. Our library didn't have any of her books either. But when a copy came up on a used books list, I ordered it out of curiosity.
I don't know why this book went out of print! My fourth grader has thoroughly enjoyed listening to it this term, and even the kindergartener looks forward to another chapter of "Boadie" (one of the characters in the book). It's the somewhat-true story of American and English children living in Lebanon sometime after World War I (some reviews mistakenly say it's set during the 1940's). The American brothers "do lessons" on their own, and their friend Dorothy, nicknamed Boadie, has a tree-climbing governess who might have stepped right out of Charlotte Mason's training college. There's a bit of a mystery involved to thicken the plot, but mostly it's a story of kids doing the things kids do, mostly outdoors, whenever and wherever they live and in whatever languages they happen to be speaking at the time. Although it isn't a book that really deals with Middle Eastern issues, it could also be an introduction to life in that part of the world.
I can't help comparing this book to several others of the same vintage I've read recently by one particular Christian author who has been widely recommended, and who also wrote a book set in a Muslim country. I prefer Crystal Mountain, for several reasons, and I know it is the kind of story that my children enjoy as well. Although it's not an overtly Christian book (the fact that the father is a missionary doctor is not stressed), there is a strong Christian feeling of caring and respect in the way that people treat each other. (Yes, I know people of other faiths or no faith at all can treat each other with caring and respect, but in this case it seems that these are people living out their Christian faith without making a lot of noise about it.) I think there's a time and place for both kinds of books; but I can't help wondering why Crystal Mountain is the one that's gone out of print. Used copies are available inexpensively online (and there is a sequel which I haven't gotten hold of yet), but it seems the kind of book that would sell well among homeschoolers if it was reprinted.