Hoser,
Actually, Freedom Arms lists/makes one themselves, and it's a pretty nice rig. It's a shoulder holster, but with a scoped gun, I think that's about the only feasible way of carrying. As for the pouch for the extra cylinder, I think that'd be a bit of a pain. Not only is that a very heavy cylinder, but there's no easy way to change it in the field. The base pin is set-screwed into the frame, and, at least on mine, the pin is VERY well fitted.
go to
http://www.freedomarms.comand check under accessories, leather scopes.
~Jim Keeney