The only place I have seen them for sale outside of Russia is over at Rusmilitary. I plan to use one of mine on a future Saiga build/conversion so I think you should be good to go. You can actually get a Saiga in Russia from Izhmash with this stock on it as an option for some of their models. Not sure about using the Bulgarian trunnion as I don't have any of them to compare to. There is a member here that posted a thread on another board and a link to that thread here about his build using one with photos. I think he liked it enough to get another one if I'm not mistaken so take that for what it is.
Good luck and let us know what you decide to do! :smile: