Select the "Bonus Items" option at the main menu to buy the indicated map in Empire Map mode for the corresponding amount of Empire points.

Agincourt: 250 Empire points
Archipelago Large: 200 Empire points
Asia Major: 300 Empire points
Bridges Large: 100 Empire points
Castles: 150 Empire points
France: 100 Empire points
Hannibal's Crossing: 250 Empire points
Hastings: 250 Empire points
Khyber Pass: 250 Empire points
King Of The Mountain: 300 Empire points
Outremer: 150 Empire points
Skirmish - Desert: 250 Empire points
Skirmish - Plains: 250 Empire points
Swamplands: 150 Empire points
Valley: 100 Empire points