Remember, possesion of corn snakes in NJ is Illegal except for "red albinos". It's a well intentioned law, but that's as far as it goes.
Eddie, are you sure they were corns and not young eastern milks? The extent of the the known range for corns in NJ is pretty much limited to the Pine Barrens area of Southern NJ. Not that its impossible for corns to be in Mantua, but it wouldn't be expected. Corns are on the NJDEP endangered species list. Unfortunately, the state ignores the fact that corns are endangered in NJ due to habitat destruction, and the limited availability of that habitat in NJ. Corns are pretty much restricted to the sandy soils that are available in the Pine Barrens. I guess that as long as the builders continue to donate money to the politicians, the blame will be placed on reptile enthusiasts.
As for places to go, Batsto village is nice and easy to get to. In addition to going herping, you can check an 18th century bog ore village. Also, there use to be a place in Jenkins Neck that offered canoe trips down the Wading River. One of the trips was an overnighter. They dropped you off, and picked you up the next day. There was a place to camp along the way but you need to get a permit from the Wharton State Forest.
There are hiking trails through both the Lebanon and Wharton State Forests. Both of these offer great habitat for not only corns, but eastern milks, black rats, Northern Pine (also listed as endangered), ring neck snakes, and water snakes.
Good luck and have fun!
Mike