People who raced bikes back in the 70's 80's and 90's and still have their old bikes are great sources of quality bikes and parts--they tended to have good stuff and maintained it well.

The trick is finding someone who meets this description, still has their bike(s) and will consider selling. I've stumbled on a couple of great bikes this way at garage sales--the bikes were hanging on the wall and not for sale, but when asked about the bikes, the owners decided to sell, at quite reasonable prices.