To return to the original request, getting hold of ballads or listening to them will be relatively easy. I recommend you start with some that have repetition and choruses to give yourself some thinking time. A couple of prime examples, one already mentioneed, The Cruel Mother, but also The Two Sisters. There are plenty of others similar. When you're ready to start delving deeper take a trip to Harvard and see if you can get into Child's library to look at some of the original manuscripts. Also check out your local library for copy of Folk Songs of the Catskills by Cazden et al for one of the best ballad books ever written.(IMHO)