I can't tell you about the housings, but high-temperature paint is sold in hardware and automotive parts supply stores, for use in restoring barbecue grills and for painting inside engine compartments. The trick will be to find one in a flat finish for the barn doors. One brand over here that is kind of popular for the high-temp or high durability thing is called "Hammerite". You can get it in a finish that contracts a little bit as it dries and hardens, creating a matte finish of tiny wrinkles. I would buy a small can and test it first, see if you like it.
"...for use in restoring barbecue grills and for painting inside engine compartments. The trick will be to find one in a flat finish..."
Actually, that's probably the easy part... I've bought black high-temp quite a few times at the hardware store, I didn't even know it came in other than flat... all I've ever bought was flat, I think it will be easy to find.
But yeah, Mark's right... BBQ grill or engine paint is what you want.
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