or maybe not . . . but I don't think you'll find any particular bar or place that particularly features young Thai men with long hair. I could be wrong, but I would be very surprised if such a place existed anywhere. Try bars that feature lady-boys perhaps; I'm not into lady-boys, but that would be a logical first step. You are looking for a type of person with a special physical characteristics. Those people exist wherever you happen to find them. Although it could be an adventure by searching for one, but personally, I don't like having those kinds of expectations.
This is sort of like looking for a place that features men who have big dicks. If there were such a place, there would be standing room only.