This is one time you might bypass your local spot. "I find that spices from dedicated spice purveyors who stake their reputation on their merchandise, rather than local Chinese markets (which are very good for many things, don't get me wrong) are a much better bet," says bushwickgirl. She gets hers from The Spice House: "wonderful customer service and quality products," she says. Caroline1 recommends World Spice. "I find World Spice has exceptional quality for the price as well as carrying things I can't find anywhere else," she says. And another option is Penzeys—top quality, if more expensive.
A final tip from Pei: "I've had better luck getting that numbing feeling using Sichuan peppercorn oil," says Pei.