Agree with the chrome plated steel crowd. As such repairing a deep scratch is virtually impossible. Polish the chrome around the scratch. Many chrome polishes are rust remover as well, like Turtle Wax brand. So get the rust out of the scratch so the silver steel shows thru. That's about as good as it gets. Short of a new rim.
I certainly wouldn't want to scuff up the chrome you'll never get it to shine again.