Three or four years ago, at FS Spa on the East Side, mamasan with poor English command failed to understand what I was asking for and said that yes she had a "boy" for me. I explained her again and then she understood, but I was surprised at the male option in her place.
While it is hard to predict whether a TS SPA would bring enough traffic to survive, a regular SPA with a TS option would make more sense. (Of course, I don't know whether the inner working of a spa, how this all fits in the Chinese or Korean culture, whether it would be workable to have a trans among the girls and so on.)