I would be interested to hear if anyone's had any luck. I tried "Thai Massage Centre NI" on Lisburn and got the same experience as above.
However, the set-up (rooms, towels, pricing, cash payment) is EXACTLY the same as many establishments in my home country where you'd 100% guarantee these services are on offer, right down to the sign saying 'not to ask for any illegal services' (which in my experience usually means exactly the opposite).
I'm pretty confident there's stuff on offer here, maybe I just need to try again!