Looking to see if a sway bar exists for 5th wheels.

The width isn't the problem, it's the center of gravity. Did you haul a heavy toy around in the old toy hauler? A big weight situated low down in the trailer will cause it to be more stable due to the lower center of gravity.

Your new trailer probably has a lot of overhead cabinets and storage.

You don't need a sway bar, you need stiffer springs.