Never seen any in PA or NJ state parks.
As noted, there are often plenty of legal places where you can camp for free or for very little money, including municipal parks and fairgrounds. Some of these places even have showers and flush toilets. There are also some cyclist-only facilities that have sprung up. Twin Bridges, MT, Dalbo, MN and Winthrop, WA come to mind. I also remember reading about a couple who established one near Republic, WA. Not sure if it's still around.