This roll bar was in my 996 cab from 2008 until recently. It's a genuine Porsche Tequipment part. I don't believe these are imported by Porsche any longer, and the new ones I see for sale are in the vicinity of $3K. I'm asking $1K.
Note that the bar is designed for a cab. There is a very similar design for coupes. I have read that the cab bar could be used in a coupe, but only if you don't have a sunroof or are willing to put up with a limited range of opening. However, all I know for sure is that it fits and works well in a cab. Luckily, the car was never rolled, so it was never tested.
This is a bolt-on installation, using 4 bolts that go in the seat belt anchors. (for some reason I seem to have extra bolts, which are included)