I don't know of any powder coating that would last on an exhaust pipe. I personally like the look of raw pipes. You might be able to find a plater that will strip the old plating off for you. As Hawaii mentioned, most platers will not want to replate them.
Removing chrome and nickel by grinding is a real chore. It would be worth a few phone calls to see if a plating shop would electro-strip them for you.
For those of you who have painted pipes, did you media blast them and paint over the old chrome?