Google Maps will do the trick, the entrance is literally right on the highway. You pull off on the shoulder and drive right into the field (after waiting in line for a few hours).
I'm coming from Jersey, so I take 78 out to 81 south at Allentown (Looks the same for you from NYC - Take the Holland Tunnel and keep going on 78 W until 81 in PA). Stay on 81 forever and watch out for cops in VA - they know we're coming. I got a speeding ticket last year because the limit goes up and down a lot and they nailed me right at change from 65 to 55.
Then take 40 W to 75 south, and then 24 up to Manchester. You'll see a line of cars on the shoulder a few miles before the exit. It's really easy.