I've started to put together a Google Map with the various known sites related to Esterbrook's history. It's not complete, but I thought some might find it interesting as is.
I've identified a second Camden site they used for manufacturing fountain pens. Not sure exactly what they did there vs. the main factory, but it was used from 1951 through 1964 when Esterbrook moved all of their production from Camden to Cherry Hill. There was a third site used for storage, and even a possible fourth site in North Camden (the source for that is from 2005, so not contemporary).
I've also identified where the English works were located. It's now a student dorm, but was formerly the John Mitchell works. Esterbrook first used Mitchell to make his steel pens under contract for the European market, then Esterbrook purchased John Mitchell outright. It's probably a fair guess to think they made their early gold nibs for the Conway Stewart and other early English fountain pens there. In 1948 they started to make the Esterbrook J pens and others in the same building in which they had made the steel pens.
I would love to find out where in Brazil, Columbia, Canada, and Mexico City they had factories. I haven't even begun that research.
I've also found a few of their New York offices, at least the address, as well as their original Philadelphia address on Arch St. It can give you an idea of how much they moved around, and how well bunched most of them are along John St.
And I've thrown in a few of the homes lived in by Richard Sr. and Jr.. I've also include the homes of three guys I think may well be original pen makers for Esterbrook. At least one, John Turner, was British and came in 1860. I can't confirm they worked for Esterbrook, but they were pen makers in Camden, living just a couple of blocks from the Factory at a time when no other steel pen makers were in Camden. It's pretty likely.
Anyway, I'll update the map as I gather more. If you have more to add or corrections, let me know, with sources and I'll add it.