[size=12]I'd second the suggestion of auctionzip.com, but I'd imagine that you're going to have to drive pretty far out of the city. If I were you, and I was using auctionzip, I'd probably set the searchable area to 100 miles from your zip code, even if you'd rather not drive that far. It gives you an idea how far you would have to drive to find estate sales that have cast iron available. It is just imagination, since I'm just not comfortable in any major cities and tend to give them wide berth, but I think you'd have better luck finding antiques in areas that aren't quite so populated. Also, if you feel like driving, look for large antique malls, not antique stores. A city antique store owner probably won't be relying on antique cast iron cookware to draw customers, but often there's a few dealers in large antique malls that specialize in it. My own experience has it that the more an antique store looks like a furniture store, the worse it is for having cast iron, and the more it looks like a barn, the better it is for good finds.
But another problem that you're going to see on auctionzip is that a lot of the estate sales that show up in searches for collectible cast iron only have one or two items, and the pictures that go along with the sale bill are often poor quality or not very representative. They like to list that they have Griswold skillets, for instance, and then show a perfectly useless picture of a bunch of stacked skillets or of the cooking surfaces of several skillets, giving you no idea what sizes or types you're looking at. Sales where the deceased was a cast iron collector usually have much more descriptive sale bills and much more useful pictures than sales where there are only a few items, and nothing's worse than driving all morning and then finding out when you get there that the few pieces that are being offered are in junky shape. But those sales are less common, of course, than estate sales where there are only a few items available.
I can't speak for NY, but I've never had any problem finding good antique malls and auctions in PA. [/size]