If you are desperately searching for a particular software package but so far you had no luck finding the right repo or *.deb package, then please take a look at treviño's web site. He's maintaining a *huge* apt sources.list on his blog.
Use at your own risk.
I have no idea what happens if you add all those many repos to your sources.list ... What I know from experience is that if you add too much stuff you may risk conflicts and incompatibilities and broken packages; this is also a good way to hose your system.
So please take this piece of advice: Only add to your sources.list what you really really need. Don't be greedy.
Here is the URL: