Gog is ideal. I own several of them, and if you are patient, they run great sales throughout the year making them very cheap to obtain (and there isn't any DRM).
To add to this, the commercially available versions of the first two Monkey Island games are not ScummVM compatible without some hackery. The games are perfectly playable, indeed, but a lot of people don't have much fondness for the visual style choices.
Luckily, the original game data files are included in the homogeneous .pak files for the games, and Monkey Island Explorer[0] can unpack them.
For both games the files are MONKEY.000 and MONKEY.001 (MONKEY2.00{0,1} for Monkey 2) and the explorer program can filter for file types making it easy. Just unpack them, add to ScummVM and away you go.
Caveat is that these are the CD versions of the games. The Secret of Monkey Island was actually "remastered" previously! The colour palette is altered slightly and the UI includes an updated inventory, with images instead of just words for items. The stump joke is removed, too (partly due to the LucasArts hintline getting calls about a missing disk #131!).
Monkey Island Ultimate Talkie Edition[1] is another project that can extract the data from the Special Editions, as well as the music and voice files. The resulting build is compatible with ScummVM, meaning you can play the original games with the updated audio.
The kids are playing Freddy Fish and Pyjama Sam on the iPad right now. Good stuff! There is just no modern equivalent of these games that let's kids puzzle like this!
but hm, that category is larger than the category of supported games ... clicking through to the "where to get" link gives a more curated list.
There are 4 shipped in most Linux distros (probably more a matter of exact license than quality alone):
Flight of the Amazon Queen - everything you'd expect from a fantasy adventure; play this if nothing else
Beneath a Steel Sky - a good game, just not a happy one
Lure of the Temptress - this was buggy when I played it, managing to crash/freeze the VM
Drascula: The Vampire Strikes Back - cringe
For anyone who cares about legality, do not touch Internet Archive (archive.org) with a 10 foot pole. That place is one of the biggest collections of warez known to man today.
Just note that abandonware is not a legal term, and the ScummVM team consider it piracy/warez. You don't get supported with problems by ScummVM if you play an illegitimately acquired copy of a game.
There ARE some games which are released by the original developers for free. Beneath a Steel Sky can even be found in the Debian and Arch repositories, for example.
