These lions can be spawned using the 'Editors' however I found it is quicker and easier to follow the method below.
From the main menu click the following menu options:Single Player > Campaigns > Glory of Greece > The Trojan War
Once the map has loaded press enter on the keyboard and type the below followed by pressing the enter key again:bigdaddy
This will spawn an unstoppable black car.
Scroll down and select the Dock and build a 'Light Transport (Hotkey: E). Once this is made, board the car on to the transport and head south to an island with 4 Lion (Alpha) ready to go.
Pink Circle on the minimap: Starting Location
Green Circle on the minimap: Lion Island
Red Circles on main screen: Lions
Unload the car, kill the lions and the achievement will pop. No need to finish the mission.