Hi Ben,
The boat I'm assembling, a Cape George 31', is supposed to have a glassed-in bobstay chainplate similar to yours, only done in bronze. The owner's brother makes them custom to order, and they are beautiful. You might give him a call and see if he can make you one--Google "Cape George Marine Works" for the phone #.
In spite of that, I opted to fabricate my own chainplate and bolt it on with backing plates--it was cheaper that way, since I was buying bronze for all my other chainplates anyway. I just purchased a plate of 3/8 silicon bronze and a smaller plate of 1/4, (I found Atlas Metals to have the best price, still about $10 a pound), and cut out all my shapes with a borrowed plasma cutter. My saber saw can chew through the 1/4" plate OK, but the 3/8" was too much for it. Starett or Lenox brand blades seem to work best. The edges can be finished with a grinder, and sanded to any polish you desire.
If you'd like, email me:
benz@yosemite.net and I'll send along some pictures of my bobstay chainplate.
Best,
Ben