I suppose the "definitive" book on Triumph of the Will is Hinter den
kulissen des Reichsparteitagsfilm by Leni ("I was never a Nazi")
Riefenstahl herself, published in ca. 1936. The Museum of Modern Art
Library in New York has a copy, and my guess is that it might be found
in other libraries.
-Henry Breitrose
 Dept. of Communication