New York State law is the same as the federal "assault weapons" ban. No regular capacity magazines manufactured after September 1994. Pre-ban mags are legal, and can be mail-ordered and purchased in gun stores.
I saw a 30-round Glock .40 S&W mag at a gunshow in Albany last weekend. $99. He was selling the Kel-Tec Sub-2000 carbine in 9mm and .40 S&W for $300.
As others have said, there are local exceptions to the state-wide law.