These weapons are unlocked for campaign after beating the game once on any difficulty. They become available on your next play through.

Unlockable - How to Unlock

Arc Charger - Beat the game once on any difficulty
Backlash Grenade - Beat the game once on any difficulty
L11-2 Dragon - Beat the game once on any difficulty
Reaper - Beat the game once on any difficulty
Splitter - Beat the game once on any difficulty