Hey. I believe they don't allow fill-ups on the spot within nyc limits (someone correct me if I'm wrong). I went to this place over a year ago. I waited about 10 minutes for him to fill up. Call to make sure they're still open, lol. Otherwise I can check for you in a week or two; I need to refill mine.
Clinton Welding Shop
Address: 40 Jericho Tpke, Jericho, NY 11753
Phone
516) 334-1377
http://weldingsuppliesplus.com/contact.html