American Civil War Shooting Association. Somewhat of an off-shoot of the N-SSA. Friendly people. Check out ACWSA.org for info and schedule of events.
I am not a member of either, just went to the one event to observe. They have smoothbore and rifled cannon shoots in Port Huron, and also shoot cannons at Camp Grayling. I just shoot in my back yard, don't have the free time to travel around the State for events. I have enough room on my property to shoot a small mortar, but not a cannon (not loaded with shot anyway). Still working on SWMBO to get on-board with a mortar at the house. She did enjoy watching the shoot at Richmond.