Dynamic Crosshair (Forgot author) does this. Search it.
http://forum.blockland.us/index.php?topic=122228.0There we go.
What do I do with that?
The problem with crosshairs in third person is that the view is on an angle. So even if you had a crosshair in third person, you'd be missing.
I had the same problem when I used DynaCrosshairs.If third person crosshairs is possible, then the position of the crosshair would have to be changed, I'm guessing.