Roy,

Michael A. Bernstein. A PERILOUS PROGRESS: ECONOMISTS AND PUBLIC PURPOSE IN TWENTIETH-CENTURY AMERICA. Princeton Univ. Press, 2001, includes some treatment of the founding and evolution of the NBER, as well as of its place in the development of the American economics profession and in federal government statistical projects, as I recall. I don't have the book at hand, so I can't be sure it is really helpful for your focus on the NBER.

Samuel Bostaph