iam trying to get info on greener general purpose guns .they were used for line throwing harpoon guns police guns and shotguns are there any books dealers etc that specialise in these guns ? or anything someone might want to add

Large quanities of Greener police guns were sold on the U.S. surplus market at one time. I picked one up cheap, had the barrel rifled, and fitted it with rifle sights. It's a fun gun and the strong action is a comfort when I am using homebrew slug loads.

I also vaguely recall seeing some line throwing guns using the Greener sold as surplus. That would follow since they are basically harpoon guns.