Large ID Timken type roller bearings suitable for this kind of service should be available as scrap from a local to you heavy truck dealer. IIRC, the KW rears had a 4" id roller bearing on the rear axles. The service co I worked for changed them based on mileage rather than condition.
Mr Cofer has alluded elsewhere on this board to a brush style suitable for welding ground made simply of a braided/stranded ground cable rubbing on a steel shaft.
My $.02 cdn