As per the heading , Is there a preferred source?
I recently had the need for a 4x4 keypad both F.P. and Symbol.
Could not come up with one yet?
4x4 keypad sounds like just a generic description of some component or part or gadget. You have to find an exact part first, or a family of parts which share enough common characteristics that someone can say if some common symbol can be used. Footprint is even more difficult because it must match 1:1 with the physical package.
Even your topic subject is so generic that we can answer “KiCad libraries”. But that wouldn’t help you, I guess.
A 4 X 4 keyboard is 16 push button switches wired to a connector in the identical manner to the keypad you intend using.
The footprint will have a connector that matches the symbol for the keyboard connector. If the keyboard is mounted on the PCB, some additional information may be required in the footprint for its mounting.
So, get your keyboard then find a suitable connector(socket) that matches the keyboard output plug.
I’m drawing all symbols myself. That way they are as I want them to be.
Footprints I search in KiCad library something to take end edit according to my needs.