You must purchase the Resurgance Map Pack for 1200 Microsoft Poins or FREE on the PlayStation 3 and PC.
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You unlock it by getting to 10th Prestige.
you can unlock it with you're first killstreak award unlock
ak47
2nd prestige
You get kills with the gun you want to unlock attachments for. If you see your challenges it will tell you what to do to unlock the attachment.