Just how much magnesium did Rockshox use in their fork alloys?
The alloy itself will be a determining factor here. Pure magnesium? Forget it, you'll never get a proper shine, and it'll oxidise before your very eyes. But magnesium alloys? You have a decent chance there.
Classic car buffs and motorcycle enthusiasts have been polishing up magnesium alloy parts for decades, with some success. Some hold a nice shine for ages, some don't. Lots of magnesium in the mix tends to be more gold in colour than aluminium, but the shine only lasts a few days before tarnishing if its not protected.
Clear coat lacquer is on option to protect the shine, but you'll probably have better results and a longer lasting shine with more modern liquid polymer sealants used on alloy wheels and paint finishes by car detailers. Something like this stuff from G-Techniq;http://www.cleanyourcar.co.uk/wheels-an ... d_878.html