I know this is an old Post, but am surprised that nobody has yet provided an answer.
Having hunted around the internet for these myself, the only thing I have found is that there have been a few of these machines restored by ODK members, but none of the members have replaced this part of the posi-traction drive mechanism. I can't even find a manual or part number for this animal.
Some people call these a drive cog, others call them a drive dog.
I now have someone looking for a replacement set for his Super Four-53 and he has explained they are replaceable and have a left and right hand thread.
Maybe the short answer is to have them rebuilt using a welder and grinder.
Photos on this link wouldn't work when I was just looking, but is the closest I may get to an answer:-
https://www.outdoorking.com.au/forum/ubbthreads.php?ubb=showflat&Number=70543
Unfortunately, the member who posted this thread is now de-registered.

Environmentally friendly recycling at it's best