There are certain key indices and websites to consult. The first is the Roud index which, if you haven't downloaded it already, you can find on the Vaughan Williams Library website. This will tell you how often it has been collected, where, when, geographical spread etc. Often this will lead you back to a printed source. Another good site is this one The Traditional Ballad Index which will give you background. The Bodleian Library has a lot of broadsheets on line at http://ballads.bodleian.ox.ac.uk/search/?query=. You could also try just googling the title, but beware of statements such as "said to be .." or "purported to be ..." as these are often fanciful theories with no proof. Remember that folk song is very poor at history. If you are researching children's songs, then there is no better reference that the Opie books. This site can give you examples of research into individual songs: http://glostrad.com/. Finally, good luck.

Tradsinger