werd, i live in manhattan.
St. Marks is basically a replacement of 7th st.
So when you walk downtown and you reach:
9th st, 8th st, then bam you hit St. Marks, and after st. marks is 7th st.
Get it?

Oh, and it is on 2nd or 1st ave.
You can even buy salvia there at some table booth thing outside a tattoo\peraphalia shop. But it is very expensive. Its 30 dollars plus store tax (so 33.35 or some shit) just for a gram of 10x
Though at the cash register the dude let me just pay 30 without paying any tax which was nice of him.

That is like the ONLY salvia store so I hope my info is helpful.
Many good headshops with hookahs and bongs and shit.
And keep scouting around the village for the more random hookah stores that sell really amazing giant 4 hose hookahs that spin and shit for only 200-300 bucks which isnt all that bad!