GOW,
This is what I know.... That cannon was on ebay 2-3 years ago. It was being sold by Fort Mifflin in PA. A collector in PA was able to snatch it up early in the auction. This same collector was on Pawn Stars before with the "Magnum PI" signal cannon.
As, for GAR cannons. Yes, they did exist. There was no common type as they varied in size and style. Pretty much whatever they could afford. Some of these were breechloaders and some were Muzzleloaders.
Now, the exact date of Mfg. is tough as most of these signal cannons did not have markings to pin point a year.