I thought I'd chime in here and offer some advice. The tickling gods have been good to me over the years, and I have been lucky enough to have had many enjoyable experiences with girlfriends, friends, as well as women that I wasn't quite as close to, so I'll share what I feel has worked well for me over the years.
Broadly speaking, I would say that there are a few key things that you want to keep in mind when you want to share your tickling interest with someone else - or, better yet, entice them to potentially explore it with you.
1) Project confidence. I can't emphasize enough how important this is. If you act embarrassed about your love of tickling, you will project that it is something that one should be embarrassed about. There is nothing inherently embarrassing about liking tickling. Yes, it isn't mainstream, and many people will not have fathomed that someone could like it in the way that we all do, but at the same time it isn't a particularly off-putting fetish, unless you happen to encounter someone that has a lot of preconceived notions about tickling (and even then you can help to offer a different perspective). Being enthusiastic about your love of tickling will tend to get you a much better response than if you introduce it as some dark, shameful burden that you carry around on your shoulders. Of course, I'm not saying that you should go blurting it out to everyone on the street; you want to pick your moments, but don't introduce it as if it is something that you have been hiding.
2) Find common ground. Many people won't initially understand what it is about tickling that you like so much, since to most it is either silly and playful on the positive end of the spectrum, or tortuous and sadistic on the other end (often depending on their own past experiences). Therefore, when you bring it up, naturally the person will want to know what you like about it so much. I find that this is a great opportunity to figure out a way to make it enticing for them as well. One approach that I have found works really well is to emphasize how liberating it is to relinquish control and be out of your head for a period of time. Many people will relate to this, since it is not at all uncommon for people to feel to stuck in their own heads - especially if you are dealing with more of a type A personality. When you present being tickled as an enjoyable, cathartic release of stress - a temporary escape from their own headspace - you can help to frame the experience in a way that they will likely not have thought of before. This is not to say that you should hide the fact that you find it sexual; just that you should also try to make it appealing to them as well. Something that they actually might find enjoyable.
3) Peak their curioisty. Again, since many people will not have that much familiarly with tickling, especially as adults, there will naturally be some curiosity on their part - especially if you follow the 2 suggestions I mentioned above. This is obviously more applicable if you are looking to actually have a tickling experience with the person vs just discussing tickling and getting the subject off your chest - but assuming that you are, I would do what you can to heighten their curiosity about what it might be like to be tickled. Can't really give too many specifics here, since this is highly situational, but I would say that these 4 simple words can do wonders in the right, flirtatious context, especially for someone that you can tell is interested but is still on the fence:
"Never try, never know..."
Finally, if you are lucky enough to find a girlfriend, friend, or acquaintance who will indulge you, do your best to make sure the experience is fun for them too. Don't treat them as a fetish gratification object. Don't make it all about you. If you have ever read any of Makugiggl's stories in the 'True Stories' section of the forum, he is a master of this - making tickling fun and exciting for the other person, and potentially sexually gratifying as well in the right context.
Anyway, hope this helps!