Ceramic header coating
As far as I have been able to discover very few companies apply straight ceramic coating. Zircotech in the UK and Swain in the US are two that advertise they are in the will do automotive headers. Zircotech apparently does business in the US if you're willing to ship. There are others in the business but I don't know if they will do one offs or only industrial production work.
Of the organic or resin based coatings, there are many choices. These use ceramic and metalic mixed in to enhance various properties. Applied Plastics has a good website and is up front with the products they offer and who manufactures them.
I started a
discussion on speed talk about the physical properties of the different thermal barriers hoping some folks with more expertise would chime in.