I just finished Texian Iliad and was reminded of the "Twin Sisters", six-pound cannon used to defeat Santa Anna's troops at San Jacinto. They were gifts to the Texians by the citizens of Cincinnati, but have been lost to history. I don't know if there are ongoing efforts to locate them, but these are priceless artifacts from Texas history.

http://www.texasescapes.com/MikeCoxTexasTales/233-Twin-Sisters.htm

Clive Cussler, the famous nautical archeologist/novelist once looked for them. In one of his Sea Hunters books, he wrote about his search. Basically, he followed a story in which the cannons, which were still around by the time of the Civil War, were buried somewhere in Galveston to hide them from union troops. This is possible, but I rather suspect that the confederacy grabbed them before that and shipped them somewhere to be used or (since they were probably smoothbore), melted them down to make new cannon.