Need part number  101553 -- hubcap for my wagon gear.   Local Unverferth dealer looked up that number, and said it's no longer available. Google search  is  striking out.  
The F&H hub company that made these hubs  also appears  to be out of business.  

It's a pretty big cap,  about 4.5 inches in diameter,  and  3+ inches deep.

I can cobble up some sort of protective device to keep dirt out.. but would prefer the actual drive-on cap.   
I wonder if other brand  500+ bushel  gravity wagons used similar hubs/caps?