In the golden days of historical illustration, artists had large personal collections of props, such as guns, watches, and tableware.
The collections of Harold von Schmidt (above), Ed Vebell, Dean Cornwell, and Howard Pyle were (or in Vebell's case, are) legendary. There were also rental agencies who served illustrators for both props and costumes.
Today, most of the business for prop rentals comes from movie producers. This video (direct link) takes us behind the scenes to one of the largest movie prop rental companies in Los Angeles, called The Hand Prop Room.
They not only have original artifacts, but they also fabricate high quality replicas and stunt props made of rubber than can be used in action scenes.
Today some of the leading art schools are assembling working collections of props, costumes, and natural history specimens that art students can borrow. This is one of the ways that traditional brick-and-mortar art schools can keep their edge against upstart online art schools.
The Hand Prop Room