You can try Bristol Bronze in Tiverton, RI.
The owner is Roger Winiarski and he can make a new cleat from your old one. Send him the parts
and he can glue them together well enough to make a lost
, then cast you a new one. You can specify type of bronze and finish--the higher the grades, the more expensive. Call him first to discuss precisely what you need, and he'll advise you what to do.
Roger purchased all the hardware
molds from the Herreshoff Manufacturing Company and keeps stock items of some of the more popular pieces of hardware