Sorry, I didn't make the connection before. Brumley's Songs of the Pioneers includes several "volumes" and they are - or were within the past few years - still available from "tourist shops" along the road. My #1 shows the ©1970. The #2 shows ©1973. They apparently are, or were recently, still in print as I got my two brand new ca. 1996 ($2.59 each) at the famous "Wall Drug" tourist trap in Wall, S Dakota, just down the road from Mt Rushmore. If the #1 was still being reprinted after 26 years, and the others are newer, there's a pretty good chance it, and the later ones, are still in stock (but I'm not about to drive the 1600 miles round-trip to check it out for you.)

This is not to say that it wouldn't be hard for most people to find, and could be worth a "few bucks" to someone interested; but I doubt if a knowledgeable dealer would consider them "rare." You never know what something's worth until you find someone willing to hand you the cash.

John