rail that affixes to the pistol grip nut

Does anyone know where to order these? I saw one a while back when i didnt have any optics but now i have a little red dot i'd like to play with. And has anyone tried it? they look like they'd hold decently.

3rd one down maybe?

http://www.gunaccessories.com/militaryscopemounts/AK47/index.asp

no thats not it, the only thing that held it there was a square cut out on the bottom that the grip nut went through