I'm using a Debian spin (Kwheezy, based on Wheezy + KDE), that came bundled with all kinds of additional packages. The apper sources list includes a bunch of extraneous ones. The distro is getting long-in-the-tooth and the maintainer has moved on; some of the apper sources no longer exist. One of these days, I'll bite the bullet and attempt an upgrade, but I'd like to limp along as long as possible because everything is rock-solid.
In recent times, I've received occasional messages from apper that one of its sources wasn't available. I disabled these sources to stop the warning messages. However, that means whatever packages were being maintained from that source are no longer being maintained. I want to at least keep my eye on security issues or possibly find another source (or uninstall those packages if necessary).
How do I identify what packages on my system are associated with a specific source (that no longer exists, so I can't go to the source to see what packages it used to contain)?