Belive it was MItchel that offered an 18" SAA cartridge version ith a shoulder stock...they've stopped offering it some time back. Hadn't known that Pietta offered the stock for the Buffalo still...thought (wrongly it appears) that that had been discontinued. Given enough time and effort, am usre you could adapt that stock to fit on other handguns...the legality of which would be up to you.
Do not quite agree with MEC, the stock makes little difference, but it is a measureable difference. From a bench, where you can pull your face back to a point that would be impossible standing, it shows a greater advnatage.
Back in 1860, they should have made the stock hollow,,,,and filled it with rum like a canteen...that way, the troops issued one would have been likely to keep it.