Rusty, we're not in good shape here
from what I understand the care at Manhattan's newish exotic pet veterinarians leaves much to be desired - so much in fact that I would not put a garter through the stress of bringing her there. I'm in Brooklyn though. You could call them and ask specifically whether they can give your snake a B1 shot.
My local herp vet here is pretty okay for anything short of surgery. Her name is Dr Jill Caruso and she's at Pet Haven, Corner of McDonald Ave and Caton Ave, close to the F train @ Ft Hamilton Pkwy, phone 718-435-6900
if either does not work for you, your best bet is a friendly neighbourhood vet who's main purpose in live is to help critters and who's willing to give your snake a vitamin B1 shot.
If you do have a car, Sean (animal rescue guy) tells me there's a good herp vet in New Jersey. I can find out where.