I just got a powder coat finish from Forrest Products in Oregon. It's a
coating that's supposed to be good to 1200 degrees. It's available in a
couple of grays, flat black, and forest green(?). They're on the web.
It's the only supplier of high-temp powder coatings I've found. It's a
bit pricey, but they will sell 5 lbs, which will last a long time.
I put the powder on a set of manifolds going on my '68 Fury. It went on
well, and looks good. Can't say anything yet about performance and it
will be a while before I get it running on the car.