Two or three more come to mind here; the museum at Quincy, Illinois is reputed to have a good collection though I have not seen it. The Missouri Historical Society in Saint Louis has a fine collection, including an M. Lewis owned, J. Small rifle. The town of Arrow Rock just west of Booneville, MO also has a rifle collection.
And, for those out west, or coming west, the museum at Weaverville, CA has a modest collection of J. Craig, California rifle made during the period of the gold rush. The museum at Exposition Park in Los Angeles has some nice KY Rifles as well.
Dick