I usually hunt the parks here in the city, many of which are historic.
The NYC metal detecting permit is FREE and can be obtained here:
https://www.nycgovparks.org/permits/metal-detector
And yes, there are a few hunts on the horizon. One this Saturday involving Rockaway Beach. Look up Rockaway Beach NEWS on google, and you will see that a huge amount of erosion has caused the beach to be closedfor the majority of the beach season last year. This spring, they are planning on dredging up that sand and reopen the beach, but for now, there are about 10 blocks worth of very old sand to search through. You can get the gist of the story here:
https://patch.com/new-york/queens/rockaway-beach-will-be-fully-open-summer-2019
Also, I plan on detecting POE PARK soon, which is the site where Edgar Allen Poes cottage (where he lived when his wife died) now lies. Last year I found a silver quarter metal detecting the back yard, and I know there is a lot more there.
The cottage:
https://www.instagram.com/p/BZWScZdBvmb/
The quarter:
https://www.instagram.com/p/BZWZuTcBoF_/
I have done other hunts this year, like looking for an abandoned amusement park in Canarsie:
https://www.youtube.com/watch?v=NvzzRVU4HWs&
But I would highly recommend Merrill's video on that (he found a seated dime, and much more silver than I did at that location when we went out).
This is his youtube channel:
https://www.youtube.com/channel/UCjXJz7GPG9L3vxAzjxoah4Q
And the videos are called "Unearthing Golden City"
I am constantly hunting Orchard Beach in the Bronx and Coney Island as well, but I do have a full time job. The two days I have to detect are normally Friday or Saturday, and so I try to reserve one of those days every week to go out. Let me know if you are interested and you can join me!