Do you still buy older games today? If so, where do you find them for sale? You can't get most of them in a major name store unless it's in a remake or collection, so what is your source for retro purchases?
During the warmer parts of the year, I sometimes go to flea markets and find some good deals there. There are people that set up there week after week selling, like a business. Most of their stuff is overpriced, but sometimes they have a good gem that is worth getting.