ArtMetal

LS, here's a suggestion: I am also in NYC , perhaps you can contact someone at Socrates Sculpture Park in Long Island City. It's the pet project of Mark DeSuevero. I'm sure there's some corten steel to be had there. Try them.
Also try Eastern Steel in Brooklyn for a small order you might have to go there and pick it up. Last but not least try some scrap metal dealers. Good luck. Janet R.