if its just a pin could you go to a machinist and ask them to make you a new one?
or is it the complete coupling thats one bang?
interestingly i just googled it and tr4 owners seem to be modifying datsun shafts to fit their own so maybe theres a supplier out there for these parts?
That is one problem with Santa Pod. The level of grip is massive so the weak link will give way. I am still using standard shafts on mine and have had about 4 break in the years I have owned it. I believe there is a stronger UJ but cant remember where I have seen them.
Another issue is with all the poly bushes available and fitted these days it takes all the compliance out of the car so therefore the shock loading is far greater as there is no rubber to take up the shocks and strains.
Just my 2 pence worth
With a Quaife diff as well