2 spring to mind
The British Folklorist by Richard Dorson pub RKP 1968
and
Anglo American Folksong Scholarship since 1898 D.K. Wilgus pub Rutgers 1959The Dorson was remaindered years ago at £1-50 per vol - but that was a long time ago
Dorson's Peasant Customs and Savage Myths also has a substantial list of researchers,
Good luck,
Jim Carroll