ive seen pics on the web of roadsters with diamond plate grills, so i know it can be done. mesa's feb 2010 catalog lists the diamond plate panel as an option for the roadster, but it doesnt give a price. its got the diamond plate for the road king at $180 tho. id assume theyd be close if not the same.
thats assuming youre ordering a new one tho. i dont know if you could order just a head shell, but you could just call them and ask.