No sites on these. Perhaps Whitaker has some.
Show some pictures here.
It is generally felt that a four inch Luger is illegal to attach a stock and shoot with it. (Short barrel rifle from the 1930 something firearms act). So show stock not attached
Value, well one is being offered on another site for five hundred right now. Likely you have a war made stock for an eight inch Luger. Pictures of both would help.