Gluten Free Restaurants in and around NYC...
I saw a bakery at a farmer's market that was advertising itself as kosher and gluten free. I don't remember the name or hashgacha, but I can check next time I'm there. Beyond that I can't think of an entire restaurant that claims to be gluten free. As Tamar said, I doubt the economics works.
I have never heard of such a thing. I think restaurants will have GF dishes, but a GF restaurant won't make too much sense, as it's hard enough to cater to a narrow Kosher crowd, but then making it Kosher AND GF would make it even less appealing to get a steady customer base.
You probably should call the restaurant in advance and ask if they have GF dishes.