There was, in the distant past, a 32 cal. or 32 gauge shotgun which achieved some degree of popularity in Europe, but it was a cartridge firearm. Caliber and gauge aren't interchangeable and I've forgotten which it was. I'm not aware of any 32 cal. muzzleloading shotguns. As stumpy said, it wouldn't hold much shot. There were and are combination guns, side by side and over/under, which are a rifle barrel and a shotgun barrel, but I've never heard or read of one in 32 cal. or gauge or as a muzzleloader, but, it seems too obvious for there not to have been muzzleloading combination guns.
Vic