The Grey-headed parakeet (Psittacula finschii) is closely related to the Slaty-headed Parakeet (which I saw in Nepal a few years ago) which together form a super-species. I briefly saw a small flock fly overhead as we turned down the road to Thung Kik in Mae Ping NP but they disappeared before I could get a shot. This species seems to be very difficult to get a photo of in the wild, not even Wikipedia has one, they just have a drawing of one!
They do have a fairly large range and Mae Ping is considered the easiest place to see them (blue dot). While you are likely to see them, expect it to be a swift fly-by!
LEARN MORE ABOUT GREY-HEADED PARAKEETS
Oriental Bird Club (only photography source of these birds in the wild I could find)
VIDEO
This is a pretty decent video of one eating even though he is partially obscured by leaves! It seems everyone has trouble trying to photo/video this bird!