With how cheap those chips are I'm not sure I see the value in sending it to the manufacturer.

I've also never seen a PCB that has the atmega built in show up without that already installed. If you want though you could find an open source board design you like and order the PCBs yourself without components... If you're up for the challenge.

I actually have a PCB design that’s exactly what you’re asking about. Its a basic board with no rgb headers or other features but I designed it because I wanted a full size with numpad (kinda hard to come by) you can order the board from a pcb manufacturer with all the parts (it includes the BoM) or you can just get the board if youd like. Let me know if you’re interested