Best you can do is paint them, as if the factory finish has worn off from improper cleaning products and incessant unnecessary scrubbing, there is no way to bring that showroom finish back. If it were me I would stencil paint then seal them to camouflage any imperfections.
I agree with Naomie. Rustoleum or Homax tub and tile paint kits. Otherwise you would need to remove them to replace them.
Maybe this project will help: