You can get a code for a STO Admiral Uniform by buying a blu-ray edition of Star Trek The Original Series Season 3:

Star Trek Blu-ray Box Comes With Virtual Admiral’s Uniform | GameLife |

Buy TOS Season 3 Blu-ray, Get Virtual Admiral Costume. | Subspace Communique

Star Trek Online Hides Clothes In Star Trek Blu-ray - Star Trek Online - Kotaku