Get a custom one made.

Bay City Clutch or Fleetpride are two I know of.

You specify the vehicles weight and power and what type of friction material you want. I picked up a custom clutch from Fleetpride for $258. The pressure plate is 400lbs heavier than stock. The disc is a dual friction (organic/ceramic). The closest thing in an off the shelf application would have cost another $100. They can also rebuild your current clutch.