In response to Robert O. Dahl's question: when you say "a source" for
old stereoscopes and stereographs, do you mean for research or for
acquisition? Your question sounded like you're interested in buying or
otherwise acquiring. Many dealers advertise in "Stereo World," the
magazine of the National Stereoscopic Association, but I don't have a
copy at hand. If you e-mail me privately, I could send you a dealer
list, if that's what you're after.