Simple - seal your garage and keep it filled with pure nitrogen. You'll want to add a big window so you can see your shiny car parts.
There are some ways to seal polished parts - clear powdercoat is one, various chemical sealants are another, and there's always chrome - but in the end if you want something to stay shiny, you have to keep it clean, keep it away from corrosive gases (tough on a car or under a hood)... and polish it from time to time.