A 24-pounder cannon is at Watervliet Arsenal Museum, Broadway, Watervliet, NY (According to this news story, the museum, closed for renovations, will not reopen. The fate of items in their collection was unknown at the time of writing (Aug 2014.) http://www.timesunion.com/local/article/Watervliet-Arsenal-Museum-won-t-reopend-5676595.php

Another cannon (3 pounder?) is in the Smithsonian Institution, National Museum of American History, 1400 Constitution Av, Washington, DC