I don’t know if I am alone on this issue or not. In my entire 67 years I have never met another human being who would enjoy conversing on my favorite topic. I rarely ever even bring the topic up but I tend to be on the alert for someone who seems they think the same way. I will occassionaly find myself engaged in a conversation that may deal with aspects of my favorite topic but never at the level I would like to get into it. I find myself searching various forums for like minded individuals but at best I have to settle for similar aspects. The topic really doesn’t matter here. Are there others that feel the same way about what they would like to talk about?
Well, it’s a big part of why I came to reside at the Dope 
Even here I can’t get as much conversation going on my favorite topics as I’d like, but the conversaton in here is more esoteric than almost anywhere else.
Have you had back luck even in here? What is “the topic” about which discussion never gravitates (or are you reluctant to say) ? If you have tried it in here, care to link to threads where you’ve brought it up or tossed it into tangentially-related discussions already in progress?
AHunter, I do hesitate to bring it up here because I don’t have any real expertise on the issue or a good use of the vacabulary that an expert on the subject might have. It has to do with human behavior, identitiy, and the concept that we can make permanent dramatic changes in the way we percieve things in a much less complicated drawn out process than is usually accepted as standard.
I am a teacher. I always get to pick.
I can relate to the OP. IRL it’s very rare that people talk about the things I find interesting. I can usually go along with the conversation in order to participate and be “part of the group” but I generally don’t have any deep feelings about it. I’m thinking that’s part of the reason I don’t participate in social media; it’s my perception (I don’t actually know because I don’t participate do I) that people are generally talking about themselves / their lives and I don’t generally care about that kind of stuff beyond a surface level. So far, this place is the closest I’ve found to any kind of well rounded, intelligent exchange.
I don’t want to go count all the threads I have started where I did choose the subject!
If I did such a thing I’d probably find that 20% or fewer of those topics got enough responses to have justified the effort on my part. Those 20% have been lots of fun but the other 80% suggest that I’m out of step with most Dopers.
To be fair, though, I probably post in way fewer than 5% of the threads I read the titles of, so 20% is probably a winning percentage. 
We know very few people who have traveled as extensively as we have, and even fewer who have actually lived in other countries beyond a short vacation stay. I don’t usually bring it up, as others can’t relate to the experience, or they change the subject to what they want to talk about. One guy even manages to bring every fucking topic around to Syracuse, NY, where he spent nearly his entire life. I try not to talk to him at all.
I can talk to anybody about anything. It’s one of those skills I had to develop in order to effectively interview people. I have to be able to ferret out their passions and converse with them about those passions. Luckily for me, I’m an information sponge and enjoy learning about new things from people who are passionate about them. I can usually find someone who will discuss one of my main interests, but what is difficult is finding someone who can intelligently discuss the eclectic bundle of things that are my main interests.
It’s probably unforgiveably picky of me, but it’s tough for me to get close to people who can’t hang with me conversationally. I don’t expect people to love everything that I do, or be knowledgeable on all the same topics. That really would be impossible. But I do need them to be able to make lightning fast shifts between topic a and topic b like I do fairly regularly.
So I understand what the OP is saying. I keep searching for the person who is wired like I am because it’s a fine and wonderful thing when we find one another, but in reality, I usually wind up conversing with someone who is good with one of my interests, but clueless on the others.
I do have specific topics I love that only come up very rarely in the course of normal life. Thankfully I like to say my piece and then leave it at that, so I only need about one go a year on some aspect of it to feel satisfied. I don’t need ongoing discussion. Usually my husband ends up asking me about one of my topics in the course of his own curiosity, or I read another book related to it and remark to him as I go, and I get to have my little discussion for the year. The subjects are not so rare that I couldn’t go out and find a group somewhere online to talk it over with, since it’s mostly just literary stuff, but I’m not too interested in doing that since I don’t want to discuss all the time. I think I’ve developed a good balance where I don’t bore anyone to tears, I don’t seem like a know-it-all on subjects experts know vastly better than I, and I still get to talk about it sometimes.
I have had two friends that passed within the last 10 years that I could talk with for hours on end. One guy was 101 when he passed and the other was in his eighties. Both were as you described, they could switch topics in a heart beat and it didn’t much matter where you landed they seemed to enjoy my passion and insert some of thier own into mst anything,
The wife and I met on a message board dedicated to what we liked to talk about. 15 years later we still talk about it almost daily.
Oh no! I’m so sorry you lost such valuable friends. They are truly rare and only a handful come along in a lifetime. I have one. We are passionate about most of the same things, although we disagree vehemently about many of them. But that’s half the fun. We talk about once a month, happily shouting at one another in perfect happiness, knowing our disagreements only strengthen the friendship more. Luckily, we are close in age, so should (God willing) be able to argue with each other for many years to come.
I hope life sends you another such person very soon.
The Internet should be the Golden Age of unusual or narrow interests. You ought to be able to find people with your particular interest, or advertise your own interest and let them find you. Before the Internet, copiers made an age of special-interest so-called 'zines possible. Before that, there were lone weirdos. 
Lately I’ve seen references to The Dark Web (and other synonyms) which I interpret to mean there are places that Yahoo! and Google don’t know about. Anybody have a good guess as to how many of those types of sites there must be and how to get at them?
Tru dat. I’m trying to think of topics we haven’t covered here at one time or another. Back when FCC regulation (your eyelids are drooping already, right? ;)) was still a hobbyhorse of mine, I could even get a conversation going about that here.