A chapter in this book:
The Cultural Experience: Ethnography in Complex Society David W. McCurdy, James P. Spradley, and Dianna J. Shandy ISBN 1-57766-364-0
contains an Ethnographic Study of Jehovah's Witnesses.
I have it in a PDF. It is 12 pages and 2.22MB.
PM me if you'd like it e-mailed.