Certainly, as Pavane suggests, the tunes in Bronson could be re-compiled from the original sources; indeed, there is a lot of material accessible now that was not available to him.  If someone suitably knowledgable were able and willing to devote a decade or two of their life to it, maybe it could be done, though as with Child, much of the value of the work lies in the accompanying scholarship; however, the problem of publishing costs remains.  I should imagine that Princeton would happily re-publish if they were in a position to do so without incurring financial risk, but that doesn't seem to be on the cards as things stand.  As I said, the first two books can be bought as on-demand reprints, though not cheaply; they would not be cheap if fully republished, either.  The fact remains that very few people actually need to own the books, and many who do never use them; there are sets I know of which sit unopened in boxes from one year to another, galling though that may be.  Meanwhile, there are, fortunately, libraries, and, yes, photocopiers.