Swain Tech, HPC, and I can't remember the other one. There are some other really good ones that aren't in the US.

There are some companies that can ceramic coat plastics, and there are some water-borne ceramic coatings that you could spray on the plastic yourself. The good ceramic coatings are plasma applied, and that obviously won't work on plastic.

You could also just apply a adhesive backed heat shield to the bottom of the air filter housing to reflect engine heat. That wouldn't block as much radiant head from the engine bay though.