I too am trying to find out more about "coach guns". Your definition is correct, that is a side by side shotgun w/ exposed hammers. I'd also add to the definition, a gun w/ the shortest possible barrels under the law.
I've been trying to find out what models are available, but I haven't had much luck, (I only started looking an hour ago however.) I'll let you know if I come acrosse anything interesting. Please do the same for me.
-john
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