Firm Feel makes their sway bars in house, they might be willing to bend up a custom one if you provide the specs.
Other than that, without the basic dimensions no ones going to be able to offer any specific suggestions.
You want frame hung or axle hung?
Width from c-c on the leafs?
vertical clearance between the axle tube the the rim.
Best advice I can offer, short of custom made, is to measure what you have and go to the boneyard and start measuring what's there and see if something can be made to work.
Remember the narrower the mounting width the less effective the bar will be and you will likely need to upsize the diameter to get back the rate you are losing.
