With no external markings, thats going to be a tough one as the were MANY local gunsmiths that would make these old rabbit ear shot guns. They would buy the barrel from a barrel maker and make these. If you take the barrel off the makers name might be underneath as that is where they would stamp them. Let us know what you find.
Around here those old guns are quite common. I bought 2 last week for 100 apiece. Most are not marked or have a lock makers name on the plates. Some just say warrented. The underside of the barrels may have some proof marks. Many were sold here as complete guns and the prices varied from inexpensive to very expensive for a nice English version. They were the go to hunting gun of the 1850s to 1870s. Some will be Damascus and the older ones usually have steel barrels. The gun pictured looks it it may be an older one and it was not an expensive gun at the time. Make certain it is not loaded. I have unloaded more then one.