Re: Help ID this Rolling Block Pistol
It is of a general type of double barrel pistol known as a garrucha. These were/are common in Brazil and other countries where the ownership of repeating handguns was restricted, often being banned for "native" populations. The double barrel was a sort of compromise, more effective than a single shot, but not as dangerous to "the establishment" as revolvers or auto pistols.
From time to time, importers have brought some into the U.S. but they have never been anything but novelties. They were have been made in Belgium, Spain and Brazil. If there are no proof marks, Brazil would seem the most likely origin.