Cerakote ceramic coating would be a good option. I notice that Milltek have just started offering this and have called it their 'Black Velvet' range :-
i have got access to a bodyshop which could do this if i wanted.
i have enjoyed doing it my way though, and its always good to be different.
its looking alright a few miles on tbh, and its holding up well. I've done around 200 miles with them and no chips as yet! the colour they've turned goes well with the defuser, which isn't too bad, i want too keen on the chrome at the end of the day. whats the point in a BSP if they leave chrome on the vehicle!