I don't want the spring loaded safety pin because that means the whole body tube is hollow and weaker, and in the case of mine, after (granted not a short period of time) 18 years of use, the back end split apart. Even so, I'd have bought the same if I had found one.
I got tired of looking. Seemed like in order to get 12 teeth, I might need to step up to a 5/8" chuck key. Bought this one with a 0.31" pilot and ground it down to 1/4". However it is not exactly as pictured:
Figured what the heck, it's only $3.39 and does have 12 teeth. It does feel like a quality key. Next I put the teeth at an angle against a bench grinder and reduced the gear teeth diameter, but that left the top edge of the teeth too wide. My *plan* was to next use a triangular shaped file to re-profile the teeth, but reaching into my file drawer, I discovered that the file I had in mind, is pretty worn out and rusty so not up to the job.
I can now use it but it's real notchy and does not seat completely. I'll either buy a new triangular file that I need for other uses anyway, or proceed with the more tedious task of using some little fine tooth file that takes a long time to get enough material off the teeth for the right profile.