There ARE NO related files; that's why your login items are labeled "Unknown". The files to which they were originally related were, or were part of the contents of, the apps/utilities that placed them, which have since been trashed.
When you installed those apps/utilities they placed login items in /Users/xxx/Library/Preferences/loginwindow.plist, and when you uninstalled them the login items remained, but with no sources, hence the "Unknowns".
Just delete the login items as I posted, and you'll be done with them.
