I was requested to make my recommendations for the witchcraft folklore books rebloggable. So here ya go folks. Really there are a lot of great folklore books out there, I highly suggest them over the metaphysical section but that's just me. And regional folklore will vary.
It took me awhile to answer this because for some reason I thought you were asking about folklore in general and that is a wide and varied subject lol.
But even folklore for the witchcraft sense is wide and varied. Since it's all regional. And generally speaking I read books on folklore and extrapolate the witchcraft from that. I tend to lean towards Scottish, Irish, British, and American folklore and traditions myself.
That being said here are my top recs:
Emma Wilby, The Visions of Isobel Gowdie: Magic, Witchcraft and Dark Shamanism in Seventeenth-Century Scotland
Patrick W. Gainer, Witches, Ghosts, and Signs: Folklore of the Southern Appalachians
Thomas Crofton Croker, Fairy Legends and Traditions of Southern Ireland
Ancient Legends, Mystic Charms, and Superstitions of Ireland
The Foxfire Books edited by Eilot Wigginton
For general folklore info and a good book for how to get the information you may want out of folklore:
Dorson, Richard, ed. Folklore and Folklife: An Introduction.
It's also a great idea to get in touch with your local college or university as they frequently have Folklore departments. You can also try googling your area for a Folklore Society, which are a wealth of information and knowledge that can be used in a variety of different ways.
Hope that helped!
Reference: magic-and-spells.blogspot.com