Chrome powercoat would be your closest finish to polished ally.
Chrome paint is an option, but the clearcoat has v.little adhesion and it'd chip in no time. (Talking about your "proper" chrome paint which needs a black base and 2k clear over the top. not the useless rattle can stuff).
Otherwise for other colours, 2k epoxy, 1k base & 2k clear if spray gunning.
1k etch, prime, colour & clear, if using rattle cans.