Michael,
    I don't know where you are, but one can go to the Library of Congress and listen to those recordings, but not, of course copy them. One of my plans is to spend some days there when I can.
    My impression is that there is a human resouce problem. I recently ordered a CD of Bascom's recordings for my neighbor and a neighbor of his when she was a child who wasn't aware of the recording. Susette and I have a house on the other side of Hanlon Mt. from Bascom's homeplace in Leicester. They screwed up the order, failed to ship and failed to notify me. When I called a student intern or volunteer was handling the ordering. I got it, but it took 3 months.

Like you I suspect there are some diamonds in the rough in those recordings, and those that are released are already well known. As said above the audience for these is small. Here is a link, good hunting.
chance Shiver

http://www.loc.gov/folklife/