Probably not a copyright issue, as most of the material is securely PD. My own perception is that there just isn't much commercial interest in Lunsford, though he is starting to draw more attention, if postings on banjo boards are any indication.

Whether the "350" total means different songs or includes different takes of the same songs I don't know, though I suspect it is the latter. There's considerable duplication among the list of his recordings in the archive, which were made over a span of close to 30 years. I don't have the address at my fingertips, but a google search for "banjo recordings" "archive of American folk music" should lead you to the on-line edition of the checklist of banjo music in the archive -- it prints out at about 100 pp (I think I have the page itself, as an html, on my computer if ya can't find it). This has pages of Lunsford entries, though I don't think it includes any of the a capella music he recorded, nor at least one fiddle tune. Still, it probably includes the bulk of what he cut for them.

The LOC will dub, but the prices for doing it are pretty high -- over $100/hr. Terms and rates are on their website.

Some of the later Lunsford recordings were made by Kenneth Goldstein, and it's likely these are the same ones that he used on the old Riverside LP of Lunsford, from the 50s, and on the early 70s Rounder vinyl "Music from South Turkey Creek." The Riverside was o/p before my interest in the subject developed, but I always intended to buy the Rounder (which also included a side of Pegram and Parham) and never got around to doing it.