How do you unlock Classified Weapons?
Solution 1:
All of the classified items in Black Ops III (including the classified weapons) are obtained through the Black Market in Multiplayer as a random drop. There is a higher chance to get them if you use the 30-Cryptokey / 200 CoD Point chest (that guarantees at least ONE item of a high rarity, which includes the classified weapons), but it is ultimately up to chance.