It's amazing what some mindless google searching can come up with. Take CDAccess.com for example. I didn't even know such a retro-gaming PC oriented outlet could ever exist, yet there it was, happily selling all its PC and Mac, retro and not-so-retro wares at pretty decent prices (usually around 20$). Highlights of the CDAccess inventory include: The 7th Guest, Zork Nemesis, Starship Titanic, a Lucasarts Archives collection and Fallout.
And to think I stumbled upon this while searching for abandonware alternatives to the Underdogs and Abandonia... Tsk.