There seem to be powder coaters on every street corner, you can look in the Yellow Pages.

30 years ago I wanted to coat my Mercedes exhaust manifolds and I sent them to West Coast Porcelain in South ElMonte, CA.
They came back black and shiny.

Only problem is that the first time I stated the engine and then let it cool down, tiny cracks appeared all over the surface. Years later, the porcelain is still there, as are the cracks.

Now, with epoxy coatings the material seems to have enough give to deal with the thermal expansion.

R.