Welcome aboard...we're proud to have ya!

'Buck and ball' is a very old concept used centuries ago in muzzle loaders, and the concept apparently worked fine back then. I have no idea if this current loading is any better than standard Buckshot or not, but I am pretty sure it would get the jib done if the shells are reliable.

Still, given the advances in modern shotshells, especially the newer Federal Flitecontrol loads, as well as the fact that you can buy Buckshot locally to train with and verify reliability of those specific loads in your, specific shotgun (something you really should do for a defensive firearm) I would not bother with 'exotic' stuff unless I was just curious. Even then, I have no idea if the manufacturer would stand behind their ammo should you bugger up a shotgun while testing it. All major US companies and several foreign ones as well have track records of QC and reliability with premiun shotshells. I cannot say the same for the 'exotics' sold in various places and loaded by God only knows who.

Standard Foster 'rifled' slugs will shoot fine in your Cylinder bore barrel...they were made for smoothbore barrels and the open, cylinder choke works well with them.

You might try the EE here and place a WTB ad...someone may have just what you are looking for. If that fails I would probably try Brownell's and see if Uncle Mikes sells a pair of swivels only, which I seem to recall thay used to but am not sure about now days.