Hi Cooter; Coastie, one of our BBers, had some 'G' shield stickers made ... believed to be sized off the originals. I don't think he had any 'rooftop' logos done but maybe. I don't know of any public domain stencils.
IF another BBer stuck their guitar in a copy machine, they could xerox, scan, and mail you something to work with. You could transfer the image to hardstock, and cut it out with an exacto knife ... you'd have to watch for size; if the headstock being xeroxed weren't flush on the machine, the image would be too large (or small?) - either way it would be out of proportion. Not saying you aren't but it would help if you were one very adept Arts & Crafts type of person to make this work - and tidy too, one screw up and ... eechh
Good luck! CJ