I can't help you with buying Sichuan pepper in New York, but my advice is always to buy in small quantities (as with all spices) and try them. Sichuan pepper loses its bite quite quickly.
I had often eaten Sichuan food before I came to China, but wasn't prepared for the stunning punch in the taste buds of real fresh peppercorns.
Surely, In NY there are Asian markets where you will probably do better than Amazon. No?