African American Folksong and American Cultural Politics: The Lawrence Gellert Story by Bruce Conforth
This book is coming out later in May. Unfortunately the price is $75.00. Doubt that many libraries other than academic libraries will buy it. Should be able to get it from your local public library through Interlibrary Loan in a few months, though.
http://www.amazon.com/African-American-Folksong-Cultural-Politics/dp/0810884887/ref=sr_1_1?ie=UTF8&qid=1367535861&sr=8-1&keywords=bruce+conforth