Look for the derelict looking boats and pirate flags anchored off. The patrols get a bit touchy if you stay in one place too long and your boat does not add to the general aesthetic, people call the cops. Be warned, sailors can sometimes be a solitary bunch and a little jumpy. It is best to make your presence known well in advance to approaching someones vessel. You would be surprised how many boat people are veterans, and strong supporters of the second amendment. It is best not to startle us

I have a hunch you might meet some folks in just about any more run down port area if you hang out long enough. Young sailors are surprisingly hard to come by. We are by far the youngest live aboard couple that I am even aware of in my area, and boaters look after one another and have tight knit community. Especially live aboard's, talk about unique bunch of stubborn individuals
A good tip would be to head down to the docks with a box of wine, and see who crawls out of the cracks

Pretty much any person making the decision to live aboard is quite "punk" if by "punk" you mean non conformist free thinkers with out-there theory's that love to drink, smoke, and curse. You may have better luck with your inquiry if you seek out "Live aboards" instead of "boat punks." If you are looking for "punks" as in do lots of drugs, overly obsessed with fashion, and get piss your self wasted on the regular, they usually end up losing their boat in some tragic way from lack of maintenance, lack of planning, or pissing off the authorities, getting the coastgaurd called, being boarded, getting busted for something illegal and having the vessel impounded. It takes a special type of weirdo to actually enjoy living aboard full time.
In new york at this time of year, most folks on the hook already sailed south for the season. Marinas with loose security and a bad reputation would be good places to start, and bars near by.