If you're rolling in cash dye-sublimation and pad printing could totally be a possibility. Just buy the factory needed for production! For those who aren't rolling in cash, you got some etching options (Glowforge for laser, X-Carve for CNC, for example). I'm not saying you couldn't send off your design to be printed (Pimpmykeyboard will do custom dye-sub jobs for a premium) it's just really expensive.
One could possibly skip all this and use some CNC/3D printing skills to create double shot molds for resin casting I guess? If you run into moar info please let us know what you find! When I signed up early this year people said DIY capacitive switch PCBs were impossible, (like Topre) and five months later someone posted progress of a fully adjustable ergonomic Topre board!