My ww2 p08 Luger has a spot to attach a butstock?

Not to long ago I got a original ww2 p08 Luger and near the bottom of the grip it looks like there is a place to attach a butstock and I only know of arty Lugers haveing that avlable to them. My p08 Luger is a standerd 4 inch barrle and the barrle and the lower frame have matching numbers so can I find a short barrle holster/ butstock anywhere. Yes I know it would have short barrle rifle laws applied to it if I get a stock. Any info would be great. Thanks