Did you check adsbexchange.com?
You can even pull up a lot of military on that site such as C-17s, C-5s, even pulled up Air Force One either as 92-9000 or 82-8000, I have seen E-4s, E-3s etc, various helicopters. The only thing I haven't pulled up are pretty much fighter jets or bombers, although I did see a B-52 once on it.
If they were vintage aircraft without electrical, then they might not have ADSB nor would they have a transponder. However you said that they were in the NYC area, so they would have to have one or the other due to all the commercial airports around there. Unless they had some sort of special permission from the FAA since it was some sort of formation flight.
I have seen formations on flightradar24 only show one plane, but there is something where they combine all transponders to one plane since they are considered a flight of 4.