Topographic maps are produced by the U.S. Geological Survey.  Suggest
that you contact them for an index.  The main address is:
   U. S. Geological Survey
   523 National Center
   Reston, Virginia 22092
They will probably refer you to the center nearest you, and my guess is that
will be the Federal Center in Denver.  Earth Science Departments at nearly
any College or University will also generally have map collections that
include topographic maps.  (The U.S.G.S. did not have a decent Internet
connection the last time I checked, but they might have by now.)
If you are interested in gridded satelite shots, the Landsat photo reduction
center in, I believe, Sioux Falls, SD might be a reasonble place to contact.
I don't have their address but you should be able to get it from either
NASA or NOAA.  Good luck.
Lou Lucke