You can purchase these at the Special Features section.

ART Part I: Purchase for 10 Intel Points
ART Part II: Purchase for 10 Intel Points
ART Part III: Purchase for 10 Intel Points
ART Part IV: Purchase for 10 Intel Points
Increased Force: Purchase for 650 Intel Points
Invisibility: Purchase for 900 Intel Points
Once Shot Kill: Purchase for 600 Intel Points
Unlimited Ammo: Purchase for 550 Intel Points
Unlimited Items: Purchase for 550 Intel Points