The Library of the Sierra Club based in San Francisco makes available
at remarkably good prices copies of photos of John Muir (as I recall,
they have at least one "field" shot and a couple of "portraits" (one
"young" and one "old" as I remember).  They also have available a
selection on Ansel Adams prints -- all proceeds from these sales of
photos benefit the SC's Colby Library...
 
Sorry I don't have the exact info (I'm far away from my desk in SF)
but call the Sierra Club and ask for the Library.  They're in SF
(area code 415) -- they also have an internet address:
 
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Tom Moritz
California Academy of Sciences
(from IUCN, Gland, Switzerland)