I did find a suitable one supplied by Graham Bantock's Sails Etc. but they only make it in stainless steel which isn't very vintage. I bought their quadrant then set about making it more appealing and brassy by soldering on brass sheet then cutting to size. I re-drilled the holes and tidied it up. The finished article looks great and only cost £19.00.
The first tiller I fitted to "Grace"
Braine setup with quadrant.
The brassed-up Quadrant