I need a 'female' 120V AC Plug / socket for a wall plate?
What you want there is an inlet and I recommend you stay within Nema 5-15. It is perfectly legitimate to connect a Nema outlet to a Nema inlet with inside-the-wall wiring. Since there is an inlet involved, do not under any circumstance connect this section of cabling to Mains power in any other way.

You want to do your inside-the-wall wiring with perfectly standard and common Nema 5 - 15 outlets and inlets.

Now, if you need to connect to IEC c-13 / c14 ends on your equipment, you can get the adapter cables necessary to go from IEC to Nema without any trouble.