Of the Child ballads, see particularly numbers 1,2,3,4,5,6,10,17,18,19,20,29,30,31,32,33,34,35,36,37,38, 39,43,44,45,46,77,78,79,113,243,278
You can look for these in the database with the #sign followed by the number.
Penguin has published a large number of reprints of very old sources including old myths, sagas, and Arthurian material.
I assume you have read the Golden Bough. There are several Arthurian websites:
For tunes to the Child Ballads, the reference is Bertrand H. Bronson, Traditional Tunes of the Child Ballads, multivolume and out of print, but available in some libraries.