I fear that the only simple answer to your question is - from someone who is breaking up their SeaHawk.
I could be wrong but I recall that there is no makers mark on the under-side of the standard SeaHawk cleat so there are no obvious clues to help the hunt for one and, certainly, I have been unable to locate even a close copy from the products currently on the market.
Hi Ben Just looked in my stash of fittings and found two cleats that might fit. One is brass with a base diameter of 8.5cm and fixing holes that are 4cm apart, top prong is 6", probably too big for the SeaHawk. The other is galvanised with base diameter of 7cm and holes 3.2 cm apart. The top prong is 4" for that one. Let me know if they are suitable. Brian 07850866467 East Devon