I saw a thread about that a while back, might have been yours. From what I could see, the airsoft stock would cost almost as much as the Rhineland.
That may not be an issues, though. Rhineland is getting some bad reviews for taking peoples' money and not delivering the product.
They have been around for a long time but the product line up and what they do/sell changes. They had this thing for 22's and before that made pistol caliber conversions for Fal's. I have thought about one of there PSL stocks.