If I Get The Call Of Duty 5 Maps For The Zombie Mode, How Many Do I Get & Where Do I Get Them From?

Me & my friends play Call Of Duty 5: World At War, The zombie mode, We are really tired of the same map so we want to buy the new maps, How much are they for and where is the exact place where i can buy it on the PlayStation Store? And even how many maps do i get? Like all of them? Or How many? Please can someone help?

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