This perk and achievement is basically just a grind fest if you do nor usually use the dual-wield feature in this game.
The dual assault rifles seem to be best for this as they quickly cut down most enemies. If you are in a stealth section, see if you can dual-wield the pistols and only use the right silenced one to kill and it will count.
The LKW kills only require 25 and the gun is very fun to use so it should not take too long to rack up these kills.