I don't have a silver bullet, but if you have a topic you're interested in, the search provided by Octopart is very good (bottom of the page), and it's not that time consuming to dig through the results. That's how I found mahmud's comment on Lisp compilers, because I was looking for discussion on HN about it.
Obviously some topics are harder to search for (for instance if you wanted to read about what HNers have said about Techcrunch over the years) but for the good and classic stuff (programming, math, etc) I think this works reasonably well.
It would actually be really cool to see what HN threads are linked to the most from HN. I bet that would be a decent way to find gold, especially on stuff you weren't specifically looking for.
EDIT: Other than Ask HN Archive, mentioned above.