It's pretty unlikely you'll find a direct replacement.. unless you can find a boat being parted out. But any machine shop should be able to create something that works for you. It could get expensive, but would be cheaper than casting another one-off.
But checking with a marine consignment store and asking around the local yards could prove successful.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)