A heck of a project to undertake. They are a cool milestone in AR-15 history, but I suspect you will have to make the stock on your own. I don't recall any companies making reproductions, just a couple of guys making them in their garage as a sort of cottage industry. If they don't want to sell to you, there's not much you can do.
Five years ago nobody was making them, the guys who wanted one were building one. Enough good photos exist on the net to do a good job. But like I say, it's a heck of a project.