Came across these sites by accident today:

http://burtonholmesarchive.com
http://burtonholmesarchive.org

The first site has links to a fairly large number of still photos taken in exotic locales in various formats, plus about 40 8x10 portraits.

There appear to be at least three books on Holmes's work, and George Eastman House apparently has a significant stash of his, and his partner's (André de la Varre), motion picture footage.

Worth a look.