Here is a tutorial on how to Buy Classified weapons at any level. (It works for any gun/attachments/equipment though.)
1. Get a friend to invite you into a Combat Training lobby.
2. Then navigate to the desired Classified Weapon. (Needs to be visible. i.e G11 in Assault Rifles)
3. Now click the weapon and when it says "BUY AND EQUIP" have your friend change back to Player Match.
NOTE:This will take cod points off your online amount. Need to be the needed level to unlock the gun in Combat Training.
Have Fun Before They Patch It!!!!