Where can I find sources for duplicating/copying historical photographs?
Many photographers, photo labs, and camera stores offer copy services for older photographic prints; check in your local area. Many stores/labs now offer digital copying, which can be quick, but the longevity of the hardcopy print from digital printers is often not as good as a traditional photographic print. Color copiers can provide copies at very reasonable prices, but like the digital hardcopy output they will not last as long as a photographic print. Finding labs that can duplicate historic photographic negatives is harder; there are very few labs that have the experience doing this type of work.
See also: Where can I get conservation help?