Jason, there were any number of double barreled muzzle loading shotguns. In both flint and percussion for that matter.
Is the G. Fisher on the receiver or on the locks? Tracking down who Fisher was would take a lot of time. Fisher could have been the maker of the gun, the maker of the locks, or the person that sold the gun. There is no way, from the little you have to go on, to tell where the gun was made. If there are no proof marks any place, it is a good bet the gun was made in the US. Sometimes the proof marks were under the fore end.
Does the ram rod go all the way to the breech, if not the gun may still be loaded.