Green thai chilies in DC?
If you mean in DC city, potentially Harris Teeter, Whole Foods, Japanese market on 17th (and U? NW). In wider area, Alexandria Shopper's Food Warehouse as well as suggestions by tommyskitchen. Normally also Eastern Market (but it's closed now until Tuesday). I substitute serranos and/or jalapeños in a pinch and have also substituted red thai chile peppers. Despite my fussy recipe following when I cook most anything, I can usually be satisfied with any hot pepper. Oh, also the Chinese/Vietnamese grocery in Eden Center.