In Manhattan they’re ALL illegal and the Constitution of the United States means nothing there.
That's not true, yet. One of my best friends regularly attends the West Side Rifle and Pistol Range.
A synopsis of (NY)state laws on purchase, possession and carrying of firearms. pdf link
I don't know about Robert De Niro, but it was reported that in the aftermath of a City Councilman being shot and killed at City Hall William F. Buckley Jr. was unable to renew his concealed carry permit.