Wasn't impressed by existing offers I banged this out. Could be simpler but at 24x90x6mm it's fairly compact as it is. Uses two 15x6.5x3mm magnets available for ~$10 for 30 on Amazon. You'll want to pause the print of the main body at Z3.8 to drop the magnets in before it covers them; and pause Letters once Z1.0 completes to change filament if you want a second color. Whole thing prints in under an hour including color change on a Prusa i3MK3 at default speeds and .2mm layer with 15% infill