Warren Muzzleloading of Arkansas offers a tremendous variety of projectiles --- balls and conicals --- in different sizes.
Check their website at
www.warrenmuzzleloading.comI don't know if I'd go with a .32 caliber pistol for anything beyond 25 yards for target work.
Back in the 1930s, many target shooters got away from the .38 Special and went to the .32 S&W Long. It was found that the .32 was a good round at 25 yards, but at 50 yards it lacked the momentum of the .38 Special bullet to be reliably accurate.
I think firing that tiny .32-caliber ball out to 50 yards --- with consistent accuracy --- would likewise be difficult. I'd suggest the .36 caliber.
Single shot pistols of .36 caliber typically use .350 inch balls. These are more commonly available, though Hornady makes .310 inch lead balls.
Don't confuse the ball required for a revolver with the ball required for a single shot.
Single shot .32 pistols, employing a patched ball, typically use .310 diameter balls.
Revolvers of .31 caliber require a ball of .320 to .321 inch.
But again, I'd suggest the .36 caliber patched ball for target use and occasoinal plinking.