There are a couple of old "wreck sites" on the reef, but any structure has long since disappeared. The hurricanes have done their work. Some cannons and anchors are visable, but not much else. Most visable artifacts have been salvaged. Any wreck that foundered outside the reef is in deep water.
There are a couple of secret sites but you probably won't be able to find a guide to take you there. It's a bit off the beaten path.