In the first place, what creeps any girl out is if you are making conversation with her while your mind is really on something else that you can get from her. If you are not interested in her as a person and genuine in the conversation, she is going to notice. Women want to be wanted for what they are, not for what they might have to give.
So what you need is experience in talking to women and being open about yourself. The best way, in your situation is, like some have said, to visit a few call girls. I live in Europe where that sort of thing is quite legal and you don't have to fear exposure or arrest. Go to Amsterdam or Hamburg where they stand in shopfront windows, find one you like and go in and ask her if she is ticklish. Most will tell you, but you need to find one who speaks your language properly and you can talk to as well. Tell her about your fetish and about what you would like. You will not creep her out. She is used to far more creepy questions. Tell her about your problems with other girls and see what she advises. Do that a few times so that you have some data to work with and then see if you can put it to use privately.
You can do the same over the internet. Find someone you like the look of, phone her and ask her if she is ticklish, as well as one or other question you might need to know about. Then make an appointment.
Your last alternative is one of the dungeons, which are certainly expensive, but where I am sure you can get a good time. I have no experience in this, as they are not really needed in Europe, prostitution being legal here. You will find a dungeon in many of the brothels.