Dustin,
6lbs, 5ozs unloaded, 70mm chambers-I'm guessing the fowler concept was either not that important on the continent, or waterfowl weren't enough of a hunting opportunity to make a dedicated gun practical in the era of these guns. With the exception of the gun John Amber photographed in 1973, they all seem to be pretty old.
Rem, that makes 6 I know of-sure to be more, but, where? Fransisque Darne cataloged them as well, but, none of those ever surfaced in the almost 2 decades my name was associated with that type of gun.
A Darne is a gun for a pretty specific crowd, and a light ten would interest even fewer in that group.

Best,
Ted