You can buy bird chilies in Asian grocery stores. I pack them in plastic wrap and freeze them in zip-lock bags for later use.
You can substitute bird chilies with other high-heat chilies. Serranos (quite a bit milder though) would be a decent substitute, and to a lesser extent, habaneros and Scotch bonnets (both much spicier so be careful!). Jalapenos would be an ‘ok’ substitute but I find that it adds too much of a green pepper flavor and not enough heat.
Let’s conclude this post with a heat remedy. Let’s face it – the sheer satisfaction and endorphin high from eating spicy foods can sometimes be followed by an excruciating burning of the tongue. Dairy can help cool you down. However, I find the best and quickest relief comes from, literally, a spoonful of sugar. Works every time.