Great thread... something I've wondered. I was fortunate that the internet was just starting to ramp up in the mid-to-late '90s, when I moved outta the house to go to college. I still remember looking up tickling video previews (Magic Touch, especially) in the computer lab, and how I had to watch over my shoulders & conceal my arousal.
Before then, I do remember scanning the library for tickling in any way, shape, or form - hoping on the chance to 'bump' into someone like me, who checked out the same book or whatever. (I came from a really small town, so I was overly optimistic when I went to a very large college). One time, I printed out some tickling cartoons, and would leave them around study areas. I had my email address on it at the bottom. I knew it wouldn't work, but I thought "what the hell?"
In the end, I think that things are not that much different. I have connected with other people about tickling without the internet. These people were not into tickling (or even knew that there was a tickling world out there), but the more I came to terms that there is nothing wrong with tickling, the more comfortable I got in talking about it with others.