Most black powder revolvers sold in America are actually made by Aldo Uberti in Italy, who are now owned by Beretta.
You would probably be more likely to buy one from there, instead of here.
Another option is to find a local dealer there who sells Ruger firearms and buy a Ruger Old Army Percussion Model in either blue or stainless steel.
These are a black powder, muzzle loading version of the Ruger Black Hawk series revolvers.
They come with adjustable sights, 7 1/2" barrel, and are a better designed, stronger gun than original type revolvers.
Here's some bigger American companies that sell the Uberti revolvers that MAY be able to ship to you:
Cimmaron Repeating Arms:
Dixie Gun Works: