The wiki article seems to support the popularity of the term "greener", at least in the minds of book and film writers!.
I have a copy of "the classic ninth edition of 1910" of THE GUN And Its Developement by W.W Greener. It is a great reference book. I took a brief look and found a reference to a famous trap competion in New York in 1891, which attests to their presence in America at that time. Greener shotguns were on the market in England in the mid 1860's, so the trap shooting reference really means that Greener's perfection of choke boring was being put to the test.
Guns of this quality would be rare, and generally found in the hands of the wealthy, mostly "back East". Ranch owners in the West would also qualify as would, possibly, some well-paid lawmen and military officers with private means.
I found NO references to Greener in The American Shotgun by David F. Butler.
Johnny, go for it!