You can contact the NASM Archives Division by writing them at:
NASM Archives Division
PO Box 37012
National Air and Space Museum
Room 3100, MRC 322
Washington, DC 20013-7012
General Museum Information: 202-633-1000
Archives Reference Desk (including still images): 202-633-2315
Film Archives: 202-633-2337
NASM Archives Division (external site).
The U.S. Air Force Museum at Wright-Patterson Air Force Base, Ohio, also maintains a very large collection of air- and space-related media.