How can I repair a rusting dishwasher tray?
The racks in virtually all dishwashers are unique to the particular models from each manufacturer. In other words no standardization.

It is possible to imagine that it may be possible to clean up the rust and corrosion on the wires of the rack. Doing so would require removal of the plastic coating that covers the afflicted area. After you get it all cleaned up you would have to apply a new coating to the wires that would also bond to the rest of the existing wire coating.

It is possible to purchase the plastic coating material specifically for this type of repair.