might try STOCKTON WHEEL they custom make steel wheels and are located in CA. Good company they made a set of wheels for one of my trucks, not a dually but I am sure they can
I have contacted James @ Weldcraft wheels. He said he can widen the stock dual steel wheel 2" or 3" to make it 17" X 8" or 9". This service would cost around $165 per wheel. Then it would accomidate a 12.5 tire. Here's their link......Weldcraft Wheels Wheel Widening Wheel Repairs Wheel Restoration