Confederate Canister was almost certainly still available in the Deep South in 1865, but Confederate Case-Shot in that region had by that time become extremely rare.
I realize your question is about ammo for the CS 6-pounder cannon at the 1865 Florida battle, but let me share some knowledge about the rather surprising near-complete lack of CS Case-Shot in the Deep South in 1864-65.
In Virginia in 1864-65, Lee's army still had plentiful supplies of Spherical Case, but Cylindrical Case was almost nonexistent. In the summer 1864 Atlanta Campaign, Johnston's artillerymen had almost no Case-Shot. Very nearly every 12-pounder shell they fired was a wooden-fuzed Polygonal Cavity ...I testify to that as a longtime Atlanta Campaign shell-hunter.)
Insofar as I'm aware, no Confederate Case-Shot has been found in Sherman's march from Atlanta to Savannah and then north through the Carolinas, except for a few converted-to-paper-timefuze CS 12-pounder Bormann Case-Shots at Honey Hill SC. Some "Sideloader" CS 12-pounder Case-Shots do show up at the battle of Bentonville NC. Again insofar as I'm aware, almost no Confederate Case-Shot (of any caliber) was found in the 1865 river-dumping at the Selma AL arsenal site, nor at the 1865 river-dumping at the Milledgeville GA Depot site.
Speaking of river-dumpings... regarding the one at the (presumably 1865) Augusta GA arsenal site... strangely, no "Sideloader" Case-Shot from there has been reported to me, but several hundred mixed 6, 12, and 24-pounder CS Bormann Case-Shots were found in the river there.
Regards,
Pete
