Well since your sway bars were stolen, you may as well take the opportunity to update the entire hitch.
Nobody here has asked you what you consider "sway" though... So, what exactly do you have going on that you think is "sway?"
You see, you probably don't have sway at all. If you had sway you would have to hit the trailer brakes to stop it. Sway only gets worse if you do nothing.
The trailer will "bobble" around on uneven road surfaces, move around a bit in wind, and you might feel a "push-pull" action from large passing vehicles. None of those is sway.