I got mine from Rutters, it is OK but I did have a slight problem in that the countersink for the retaining screw was too deep so the screw bottomed in the blind hole. I also bought a new pawl but that had to go back as it had been incorrectly machined.
Here's the link for the later quadrant, more expensive than suggested by Arwyn.
https://mogparts.net/product/handbrake-quadrant-ratchet-late-cars-with-handbrake-warning-light

1956 Plus 4 4 seater