HijacK: I want to contribute to this project of getting games with scattered rights on GOG as well. Any indication how I would be of help?
Some basic recommended steps, though not rigid guidelines:
1) Find a game you are passionate about that would make a good release on GOG, ideally one which isn't already well-known and unlikely to need (or respond to) a third-part effort to secure. So NO on
Diablo, and YES on
Ambermoon, for example.
2) Mention the game here, to see if anyone else has already researched it. Even if not, they can possibly provide information about the developer or publisher, which will let you know if there is somewhere to start looking, or if you are chasing a known dead-end. (In the case of some publishers they have been acquired via mergers and buyouts by large companies which either have an established relationship with GOG, or which appear not to want one.)
3) If your game clears those hurdles, start researching it. Sites like
Mobygames can provide developer and company information on many titles, and these can give a place to start. Sometimes it's a matter of finding the developers' names and doing a web search on that. That's how I got in touch with Mev Dinc from Vivid Image, for example.