for a convertible... um I honestly am not too sure. genuinesaab has ones for hatchbacks, If you call Nick T. on genuinesaab.com I know he could custom make one for you if it isn't listed in the catalog. Try partsforsaabs.com too, they might have one. If I was you I would get the anti roll / anti sway bar from genuine, you will feel a difference in "flex"
And to agree with Wayne here, getting flexing in a 9-3 vert's rear is crazy, must be pushing it which I like. I know I have a little flex back there, for the record Wayne the hatchbacks you will most certainly notice a flex when cornering hard, I just don't want to lose hatch space by putting the strut bar in.