I've had good luck with bbq grille paint in the past on mufflers. It may need re-coating once in a great while, but it holds up pretty well for a working tractor.
I have also used VHT paint on several exhaust systems as well. Most recently on a 72' Honda CB750 4 into 1 Yoshi header and so far it has held up great.
Thankfully this place (link below) is 20 minutes from my house, as I don't think you can just stop down to the auto parts store and pick this stuff up. I also used the engine enamel on a few CB's that I have restored over the years, and it holds up very well.
http://www.caswellplating.com/vht/vht_high.htm
Jeff (teet)