South Amboy is Bortle 6. Decent astrophotography would be at most Bortle 4, and that is with photo processing using stacking.
For Bortle 4, the closest is West North West of us, from Ken Lockwood Gorge Wildlife to Voorhees State Park. 50 mins away. The Wildlife area may have too many trees, so the best is to look around plain fields, baseball fields, Voorhees High School Tennis courts to set up the telescope. I've marked Ken Lockwood and the high school tennis courts on google map. Basically anything Westward from this is Bortle 4.
The alternative to West is South, South of Rt. 70, by Brendan T. Byrne State Forest. At least 1 hour drive down there.
Bortle 3 is not possible in the vicinity as the closest Bortle 3 is North pass Port Jervis. I marked the closest one at BSA Camp Aquehonga, by Fox Lake. Any camp grounds, lakes around that vicinity should be Bortle 3. Check the light pollution map to confirm.