The Dover reprints of the Child Ballads contained a couple of dozen airs (tunes) at the back of VOlume 5.
The Bronson is out of print. It came in two varieties: a paperback abridgement containing about 500+ pages of lyric variants and tunes, and the unabridged 4 volume hardback edition. Used bookstores or your library may have copies of the above. (You can perhaps borrow and photocopy a library's copy?). There is a long term plan afoot (according to Dick Greenhaus) to digitize all of Bronson and mount in on the web, quite possibly as a n adjunct to the Digital Tradition. Needless to say, this is going to take a pantload of work before it becomes a reality.