You can still buy a lot of the lucas-arts games (especially Day of the Tentacle and Sam and Max) that work with ScummVM. There's a few you can't easily get hold of, but officially they're still for sale (you can order them straight from lucasarts, I think, or something similar) so its rare to find Abandonware places to get the games from. If you're really desperate, you could always try IRC... Efnet has a few chans based around that sort of stuff... but be prepared to be shouted out if it turns out they support the companies and the games are relatively easy to get hold of; they're classics, imho. You may as well buy them; only really resort to abandonware if you already *did* and your floppies have gone missing etc. (Its happened to me a couple of times... I had a white-label copy of Fate of Atlantis that's vanished into obcurity... very very annoying).
There's usually some people out there who are willing to help if the worst (i.e. vanishing disks) happen.
Thanks...