I've thought about this some myself. I did see a rig at Dixie Gun Works site a while back . If I remember right, it was a belt with a slim jim holster, knife sheath, and a pouch for the flask , balls, and other stuff.
I finally just ordered my 1st holster for my navy from Track Of the Wolf. I'm getting a plain brown civil war style that has the flap. I like the idea of the extra protection that flap gives the pistol.
In Josie Wales he carried 3 braces of pistols,because of the time involved in reloading. (plus how much powder, ball ,and caps are you gonna lose trying to reload while on horseback?)
I intend to get a pouch of some type for the ammo. In it will be a cylinder type flask made of plastic (it's light, and I don't think black powder will make it corrode the way I've seen it do to my metal flask), inline cappers, a container of lube (Gatofeo recipe) ,and another with wads. Now when it comes to the balls, I wonder if anyone has ever thought of or heard of some kind of dispensing container. I'm thinking something along the lines of those change makers that vendors wear. Just flick the lever, and 1 ball at a time is dispensed. The only other things in it would be a set of screwdrivers only for that pistol, nipple wrench, a rag,and a cleaning rod with bronze brush,and jag.