Find packages that are no longer present in the repository

I want to clean my system out of old packages. I can use rpmorphan to find orphaned pacakges, but how do I find packages that are not longer present in their vendor repository?

YaST > Software > Software management and use the Package groups view. Somewhre at the end of the list is an item Orphaned packages. Does that work for you?

I use the yast package manager. If you list all installed packages there,
the ones where a newer version is available are drawn blue, the ones where
only an older version (or no package) is availabe are drawn red.
I haven’t found a filter, so you have to scroll through the list.