Rustoleum Professional is a high quality, trusted brand. A second option is Conco Pro Industrial. Make sure to get the same brand primer, too, and let it dry/cure completely before the color coat.
DTM ( direct to metal) is best, but if you use a primer that is good for metal, you can use an ordinary latex exterior paint. Make sure you prep the surface and follow instructions
Rustoleum. They have spray and brush on.
Ditto what Don said
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