Available in GW stores on May 20th and 21st 2000 as part of the GW 25th anniversary celebrations. It was also released in the Heroes of the Adeptus Astartes box.
There is a second Emperor's Champion, which is not limited, that was released as part of the Black Templars armyit is shown below the limited version. Black Templar Captain Draco was also described as the Emperor's Champion on the 2000 Black Templar army box.