Erotic massage studios aren’t the most popular way to spend time in Istanbul. The city was filled to the brim with those about 10 years ago, but studios started disappearing. There just might not have been a market for that. You can still find the occasional happy ending here and there. But they are few and moving from one place to another quite often.
Honestly, you’re better off looking up an escort that also does massage services, on one of the callgirl directories.