Try this, just take the texture off of it.

http://www.sharecg.com/v/16240/poser/photoshoot-backdrop?division_id=11

There's some others there as well, just have to hunt for them.  There's a whole photo studio there, I think.    Also, http://nikeimage.hu/ has a great set for studio type renders including nice curtain backdrapes.

PS - If you want something white to cast shadows on, you can also just load up the high-res plane primitive and scale it up for the backdrape.  You could even bone it or use a magnet to bend it if you like.