Sometimes the keywords you need to find the most useful articles aren't always the ones you think they might be.
A keyword like proverb, for instance, might fall under the category of folk speech, or the keywords costume or folk art likely will fall under the category of material culture. Be sure the look at the overarching categories that many of these titles provide (particularly the books and encyclopedias) to determine where your topic falls.
The Folklore Reference Guide also breaks these down into convenient categories.