There is really no way to repair rusty chrome, short of replating it. The appearance of rust means the chromium plating has eroded to the point that water is getting to the underlying steel.
I've noticed a couple of 4Runners here in the Rust Belt that "repaired" their rust problem by simply repainting the bumper black in the rusted area. Both trucks had it done in a very professional manner, and it was decent looking and didn't really catch your eye. This at least forestalls further rusting.
-Karl
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