Eagle model for TO-220F-4L
SnapEDA to the rescue!  Go to their website and type in KA78RXXC into the search box and click on Search.

Comes up with six parts, several in the TO-220F-4L package.  Click on the part #, and then the orange Download button to select an Eagle footprint.

If a dialog box comes up saying "Converting file...", that will be followed by a Save File As dialog and you can save off the .lbr file.  If when pressing the Download button and selecting an Eagle footprint and nothing happens, there is no footprint available for Eagle.

What amazes me is you can enter a generic name from the top of a datasheet (like KA78RXXC) and it will come back with a list of specific parts (e.g. KA78R15CTU).  Pretty good search engine!

Usually a great free source of footprints -- however based on a comment below, it turns out the footprint they have for this particular part is wrong -- should be a TO220 with 4 leads, but they show only three.