Hi, D8PETE.
I think you will find that ALL Cat scrapers and dozers ONLY used 1/2" cable all around - except for the apron lift ropes on their scrapers. The reason they used heavier ropes for the apron lift is that it was only a single cable attached to a sheave block that was part of the apron/ejector system.
Look for someone who has a dragline or a cable crane which uses 9/16 rope and ask if they can cut you off what you need. A crane hire company that uses cranes with cables might be a good place to start.
Just my 0.02.