Just to note, in case it comes up: sharing websites that host ROMs or other game dumps (for emulation of otherwise) is a legally gray area and therefore should not be discussed on these forums. Thanks!
I agree with @newmodels - Amazon and eBay are both stores where you might be able to purchase old games. Additionally, some game producers sell games that are compilations of their older titles (Sega does this). Finally, you may be able to find digital versions of old games that you can purchase on Steam or GOG (Good Old Games).
