I get dandelion greens, endive, escarole and mustard greens from the grocery store (wegmans, not sure if they are in nyc) and grow weeds on trays in the windows. I can also get cactus pads from wegmans. Sometimes if you ask the grocery manager they will start carrying things they don't normally.
For vets, I have always just called around different offices and asked if they a) see reptiles and b) have much experience or are willing to learn. It took my a while to find a vet I liked, I went to a few who claimed to be very experienced and certainly were not. One of the reptile "expert" vets I went to wanted to give my box turtle vit. A shots for a respitory infection . . . I said no thank you and haven't been there again. The vet I go to now didn't know a ton about reptiles before I started going to her, she had seen a few but didn't consider herself very experienced. Now she is great. I told her I had several reptiles and asked if she would be willing to learn more and be my vet and she said yes, and she has not let me down. If she has any doubts about something she calls someone else to get advise (usualy cornell).
Anyway I think the best way to find a good vet is to call around and talk to them. Even if they are not yet experienced they may be willing to learn more to be your vet.