Do you want to get rid of these packages where you don't have a source for? Then install apt-show-versions and give apt-show-versions | grep "No available" | awk '{print $1}' > list-to-delete.txt
and then apt purge `cat list-to-delete.txt`
This will delete all packages which are no longer found in your repos. Keep an eye on the list before purge the packages, maybe there are packaes which you want to keep. If so, delete them out of the list.