Is there a way to find these rogue files even if I have long since deleted apps and don't recall what apps they were?
You could search through the following folders and may identify some of them, but not necessarily all:
/Users/username/Library/
/Users/username/Library/Application Support/
/Users/username/Library/Caches/
/Users/username/Library/Contextual Menu Items/
/Users/username/Library/Internet Plug-Ins/
/Users/username/Library/Logs/
/Users/username/Library/PreferencePanes/
/Users/username/Library/Preferences/
/Users/username/Library/Scripts/
/Users/username/Library/Widgets/
/Users/username/Library/Workflows/
/Library/Application Support/
/Library/Caches/
/Library/InputManagers/
/Library/Internet Plug-Ins/
/Library/LaunchAgents/
/Library/LaunchDaemons/
/Library/Preferences/
/Library/PreferencePanes/
/Library/StartupItems/
As you can see, it's much easier to do it at the time you delete the app, so you can simply search by the app name, files installed at the same time the .app was installed, etc.
I'm aware of that, but it removes more than simply dragging to trash.
Yes, barely. It basically removes the .plist and a few other files/folders, but leaves the majority behind. AppCleaner missed 11 of 17 app related files, most of them much larger than the ones it removed. Of all the removal apps tested, only AppZapper was worse.