Business directories: The NJ State Library seems to offer some resources about NJ businesses. A visit to that library (and conversation with librarians there) might be necessary
Local news media:
The Library of Congress's Chronicling America is a treasure trove of historical newspapers. On the site's home page, try limiting by publication year, state, and topic.
Genealogy tools [Our options are limited on this front, but I'll keep exploring]
"Trenton Illustrated by Ellwood Parsons Robbins was published by H.R. Page & Co. in 1891. It includes historic photographs of Trenton, including buildings, streets, parks and scenic views." (NJ State Library)