If you haven’t already found it, be sure to check out the History of Props: A Timeline of Props and Product Usage. If your show is set in 1879, and you need to know whether toilet paper rolls had perforated sheets*, then this is the site for you.
Also, if you head on over to the Designboom history page, you can dig through any number of other historical product timelines, such as the history of shopping carts, the origin of rocking chairs, and a short history of anatomical maps.
If you have any other good historical research resources, let me know. Good research is every prop person’s duty.
*perforated toilet paper rolls were first produced in 1877.