You will need a very clean surface to begin with and will have to follow the steps recommended by the paint manufacturer. One that comes to mind is VHT. Pep Boys or Autozone should have it in a number of colors.

A motorcycle shop will have PJ1 Hi-Temp exhaust paint, probably in black but they may be able to order others from their suppliers.

If you pick up a copy of Hemmings Motor News from Barnes & Noble (magazine section) there will be a number of sources in the front section.

Hot Rod magazines will have sources for exhaust coating services, both external and internal. Both types will aid in heat dissipation and help in lowering temperatures, but more expensive then painting.

Tim