That's because the Star Annihlator doesn't exist. The Empire, mighty as it was, could barely afford to keep it's seven Super Star Destroyers running and pay for the Death Star's operation alongside their planetary interests. The Annihlator was just a concept which was to be built after the Sun Crusher, Galaxy Gun, and Death Star augumented Palpatine's fleet. With his death- multiple times- and the destruction of the doomsday devices already built, the Annihilator project was not only scrapped and abandoned but utterly forgotten. It had never garnered many resources anyway, and any sane warrior would have been just as content with more of the battle proven leviathan known as the S. S. D. as they would with a relatively useless behometh of ridiculously large proportions anyway.