Where could I find a large corpus of people having real conversations, preferably followed over a long term?

This seems pretty good.

I was wondering a, if people tend to fall into some category more than others b, if there are more such categories c, if overemphasis on one behavior is a significant factor of mine, (and presumably others') social skill deficit

It's probably not that useful to think about this in terms of categories. It would be better to think about what makes a conversation great and to find out what is missing when you end up 'just chilling out'.

Let me know what you perceive to be the difference in your conversations that work and the ones in which you end up just chilling out.

Here’s some background information to help you out with that. Conversations are a type of speech exchange system that involves turn taking. When you are having your turn, i.e. speaking, this is referred to as holding the conversational floor. A conversation that progresses past the initial stage, referred to as small talk, will have longer turns in which the content is free flowing and natural. One of the main things that differentiate conversation from other speech systems like interviews is that the turns are best when they are somewhat balanced. Conversations thrive when the turns are natural, build on previous turns and allow multiple avenues for future turns.

Based on what you have said, I would presume that your conversations that don't work tend to involve short turns as you keep asking them questions and they give short answers. When conversations sag and die, it will most likely be because of minimal responses, i.e. short turns, and no free information that the other person can use to take a future turn. In fact, this is how almost all conversations end. That is, with the exchange of ritualistic small turns, e.g. “Ok, cya” -> “Yeh, bye”

In general, I think that a good conversationalist is someone who is good at doing conversational work which is all about ensuring that the conversation will continue and that the turns will become more expansive and natural. Some aspects of conversational work include:

• Asking questions (preferably open ones which lead to longer turns or follow up questions which show that you’re listening and care)
• Providing answers
• Introducing new topics
• Picking up topics
• Telling good stories
• Helping good stories
• Helping others to be able to ask you questions, i.e. offering lots of free information. For example, if asked what do you do then it is good if you can provide enough information to allow them to expand on what you have said. Don't just tell them your role, but tell them what you do day to day and why you love it, or don't.