I've been fixing old Honda Supercub keys; one had the ignition key broken off below flush with the switch, and one just had an old, old key that I wanted to get a fresh replacement for BEFORE it became another broken off flush one. No locksmiths in town with the right motorcycle blanks so it became time for Uhmerican ingenuity to kick in. Got the switch off the bike (another whole story in itself) soaked the key fragment in the switch with WD40, held it upside down, and spanked it with a hammer, making sure it was in the "Off" position first (could still be turned with a screwdriver). Ultimately I saw the fragment coming out and as soon as there was enough to grab with a pliars, it got removed. There was enough for the local hardware store to duplicate it from, after we dug through all the blanks and found a Briggs and Stratton blank that worked! It didn't work the first time but only because the "stop" that governs how far in the key goes into the switch was off (had to guess/leave a bit extra length because so much of the key was missing). Took a lil bit off to move that stop and VOILA!
After that success I was in my locksmithing stride... went back to the hardware store with the old worn key from the other bike and dug through blanks again, as it was completely different. It had a completely "flat" backside- no grooves- but I found a blank that was similar enough that I took a shot at modding it. They let me take the blank home and I took one ridge off the front side of it with an air grinder and 2" disc; the backside has a groove (while the original was flat) but I figured the mechanism would ignore that, and after sticking the blank in there, found I was right!
Went back to the hardware store to have it cut and VOILA! again.