I have answered a question here. It is the only answer to a reasonably up-voted question (+7), but it has not been selected as the correct one. Short of tracking down the original poster, is there any way to 1) get it marked correct or 2) increase the chances of it getting marked correct in the future?
Nope. Especially since the OP deleted his/her account.
Sorry about that; but the only person who can mark an answer as accepted is the OP.
"Accept" - that little checkmark - does not mean "this answer is correct."
It just means the author of the question accepted it. Hence the name.
Folks accept all kinds of things. Things they find helpful, or reassuring, or funny, or insightful, or don't like but are convinced are unavoidable...
Sometimes, folks accept the truth. But there's no guarantee that something is true just because someone accepts it. In particular, if there's no actual problem being solved, the asker's opinion on answers means very little.
Fortunately, the asker isn't the only arbiter. Anyone with a bit of useful participation on the site can vote on answers. If your answer is getting up-voted, that probably means a lot more than the checkmark.