You might be better off to have the gas check shank removed from the mould then use a PB gas check maker which is or at least was available.
if the shank is 0.419 you are limited to very thin material anyway. At least if you got the gas check shank removed you could get PB checks of standard size:
https://www.sagesoutdoors.com/44-cal...se-gas-checks/
Pat Marlin's makes PB dies:
https://patmarlins.com/using-checkma...ain-base-dies/
Or you could get an Ed Smith or IDZ gas check maker made to produce PB checks yourself as crandall crank above says. That shold work for your odd size shanks too with correct material thickness.
What is the mould(s) with odd size gc shank?
Longbow