You have two ways to go...
You can use regular automotive single-stage paint with a flattening agent, or, use rattle can.
I have had good success with using Krylon semi-flat black as a base, and then applying Armor brand semi-flat as a top coat. Sounds cheesy, but it really does work well. The Krylon is just a little too flat, but covers very well, whereas the Armor doesn't cover well, but has that "just right" look. Just make sure they're VERY clean before spraying, and leave as much of the original paint on it as you can, unless it's peeling.
You could try powdercoating, I guess, but might be kinda spendy depending on rates in your area. We did a '78 Chebby truck for a guy, he had all the inner fenders/core support coated, came out very nicely. He said it wasn't as expensive as he had been lead to believe.