For the Gold Box games, search for the Forgotten Realms Archives on Amazon or Ebay. A few years ago my dad picked up a collection of all three of the sets in a little collection for like, 10 bucks. I could never get into the older ones (too difficult, I think), but Dungeon Hack was, and is, one of my favorites. On the downside, it can be a bit difficult to get them working, and some of the games use wheels, and some of them use the 'check the word on this line on this page' protection, and it doesn't come with a manual, but the keywords are in a text file on the CD. A bit of a pain, really, but sometimes, what can you do. Besides buying them and then downloading a cracked version.
I don't think these are all the Gold Box games, though, but there are some of the really big names, like Pool of Radiance.