I've sent some exhaust parts (home made headers for one project and and a motorcycle muffler) to Affordable Exhaust Coatings here in Phoenix with good results. Would use them again. There sister company Affordable Powdercoating has done good work as well. But the powdercoating won't take the heat. Have to do the exhaust coatings for exhaust work. Lots of color options.
I hope they are still around, have not had any projects that needed anything in several years now.