Hello
At some point I must have hit a concrete block with my right locking hub and the knob that we twist to lock/free (#1 in diagram) is broken off.
I have found another cap that can replace the cap on the damaged one, but this one works differently and I have to find a way to integrate it into the old one's lower part. That is why I need your ideas.
Please take a look at the drawing bellow.

To lock we need to push the brown diaphragm (3) down and to free the diaphragm should move toward the cap.
When I turn the knob (1) the entire green section (2) rotates by half a circle. As you see it has a curved groove (notice 2 red arrows showing difference in height of grove.
I have to build something that fits between the green and diaphragm that is held in the groove. As grove rotates difference in height should push that thingy down pushing the brown diaphragm in (locking).
If you have any ideas or know of another device that work on this principal I would greately appreciate your suggestions or a photo or drawing.
Thanks in advance

Good reason to take em both off and fling them in the bin

What make are your free wheeling hubs - there are some service kits available for some of the later versions which may have what you want. This is just an example here
Series Land Rover free wheel hub service kit GLR121K | eBay
you may need to search using the manufacturers name as I expect they might all differ slightly. Failing that, I expect someone will have a set you could rob some spares from as a lot of people seem to hate the things and remove them, as per the comment above. Cheers..Ian

I would either junk them or get a used set off e-bay. You could spend a lot of time trying to fix it and never be sure its OK.