One of the best sources for games like this are offline video game shops with bargain bin sales. This is the market I used to sell in and it was quite common for use to pick old classics in bargin bins for 2 dollars and resell on eBay for up to 50, depending on the game and the condition. You have to know your games and understand your market, but certainly opportunities out there in the field if you are able to do the searching.
You'll struggle to find well priced online suppliers, they are the ones that have already found the little gems and are now selling at retail prices.