Interestingly enough, I'm currently engaged in writing about Robin Hood, and I have a friend who is a published Robin Hood scholar. As noted above by Nerd, it is almost certain that the "Geste" was never actually intended to be sung, but was a sort of organically grown epic; that said, it is the oldest extant INTACT piece on Robin Hood to survive (earlier examples are fragments), and is thought to date from the late 15th/early 16th century.

An attempt to record even(!) 250 of the collected Child ballads would be an astonishing undertaking, and would inevitably involve a certain amount of eduacted conjecture as to the "correct" matching of tunes w/lyrics; but OH, what a wonderful thing it would be to have!