It is now possible to get weapon variants as rewards for completing Contracts and Orders.
This week there is a Weekly Order 'SMG SKILLS' that involves getting 100 kills with a silenced SMG weapon. The reward for completing this order is the HANDLER variant of the M1928 SMG.
From the Quartermaster, there is a STEN CONTRACT that involves getting 15 headshots with an SMG with a time limit of 1 hour and 25 minutes. The contract costs 4,000 Armory Credits and the reward is the STEN SMG.