(re: Old Games) If you’re after any Sierra adventures released since around Kings Quest 5 I’d recommend eBay as I managed to get every Sierra talkie CD adventure off there this year, some of them really cheap.
Do you want the games to play or to actually collect them? There are other ways of getting the older games, like Space Quest’s 1-5 are available on http://www.spacequest.net. Using google you can find tonnes of places where can download them. E.g. http://alcor.pe.kr/games.php