Try either naval jelly or muriatic acid.

Barkeepers Friend.
Wet the spot, sprinkle heavily with barkeepers friend...let sit and rinse....repeat if necessary.
Linda C

Whink. Squeeze enough to cover the spot & it will disappear in mere seconds, then rinse. Works on clothes, tubs. etc. too.

Suzi

If your rust stains are like mine(large patches from the sprinkler system) which is an ongoing project-use Rust Aide. I buy it by the gallon and have a liquid fertilizer sprayer that is just for rust stain removal. Like Whink, it's a contact product. If you do use a sprayer, be sure to run water through the hose and nozzle because the parts will corrode.

This sounds silly, but try Coca-cola, you know good ole plain Coke. Pour over the stain and let sit, then use a brush to clean, then rinse. Should be beautiful! And it's cheap, too!