There is on-paper documentation, in the form of CS Ordnance Department receipts, that several Richmond VA foundries (Tredegar, Samson & Pae, and Eagle Ironworks) manufactured sideloader Case-Shot cannonballs. The Fayetteville NC aresenal probably also did. There is "field-recovered" evidence that a Selma Arsenal area foundry produced at least a few sideloader cannonballs.
You didn't ask about cylindrical sideloaders... but in my opinion, some of the varieties of Read Sideloader Case-Shot were manufactured in the Deep South, and at least one version at Selma, in 1863.
Regards,
Pete