I use Thai Green chillies in my cooking. I find that it matches the closest in taste and spiciness to our very own Indian green chilies. (Even though the ones we get in India are way better, we have to settle for this in the US :( .... )
These are available in the Indian Store or the Korean H Mart.
As soon as I come back home from the market, i don't wash them. I just pluck off the stems and store them in a dry, airtight container. And when you need it, just wash them use them.
This lasts more than two to three weeks.