Both the 12" and 13" seacoast mortars were built as model 1840 being delivered in 1842, from the Cyrus Alger Foundry near Boston. Only two of each were built and apparently none has survived. They probably remained in the north as they were essentially test weapons and achieved poor results (bursting). They were not repeated in the U.S. Ordnance construction contracts. Page 11 of the book "The Big Guns" has plan of 13" mortor.
The 10" Seacoast Mortor of same design had better results and 35 in total were built as M1839 and M1840 models by four foundries. Only five still exist today all in New York state.
Ron