Asian groceries or online. I have a Thai grocer by me, in Chinatown. Maybe you could call a Thai restaurant and ask if they buy locally.
I've got a new rub for brisket. It's Sumatra coffee beans, chipotle, brown sugar, onion, garlic, dried Kaffir lime leaf, and salt (not in that order) all pulverized to a fine powder. You get all kinds of hits from this that are perfect for brisket. I'll use another pepper as well to kick it up and may tweak it, and I will attempt the actual brisket soon with pics. Mmmmmmm brisket.
I call this rub Brisket Buzz™.