Welcome to GH
I think we need to clarify some things before jumping in with where to buy.
Are you thinking RGB backlighting? RGB LEDs require four wires going to each LED (one to control each colour plus a ground or power) and this is why you don't see many (any?) handwired boards with it. Most backlit boards (even single colour) use a PCB to keep things tidy, you just need to solder switches, diodes and LEDs into it.
This gives you two options - find a PCB which can be built with the layout you want, or design your own PCB and send it off to get the real thing made. Same applies to the plate. Do you have a custom layout in mind?
Another thing with backlighting is that either the LEDs go in the switches and standard switches are opaque black so the light only shines out of one side so for the best effect RGB boards use clear switch tops so this doesn't happen. The other option is putting the LEDs on the PCB between the switches, but with a metal plate you won't be able to see them...
Take your time, this will not be a cheap project so it's better to get exactly what you want than get something not quite perfect quickly
