The primary resource that you are referring to may be an article written by Jonathan K.T. Smith the original of which is in the possession of the Arkansas History Commission.

Like you I believe that the Institute was in operation at least through 1860. A.M.I. had three cannons - two six pounder cadet guns and one twelve pounder bronze howitzer, all made by the Cyrus Alger Company of Boston, Massachusetts, and all inscribed with the school's name. Alger also produced four cadet cannons for the Virginia Military Institute and four more for the Georgia Military Institute all of which also were inscribed with their respective school's names.

The fact that all these guns were engraved points to their being owned outright by the individual schools. Why then would they be turned over to the Little Rock Arsenal if the school closed? Cadet cannons are light which resulted in a terrific recoil rendering them barely fit for use in combat. The U.S. Army would have no use for them except as training impliments. It would have made more sense to sell them to another military school.

It may interest you to know that another A.M.I. button was dug about a year ago from the Camp Bragg area west of Camden. Why none have ever been found around Tulip is a complete enigma.