Aliens Fireteam Elite: All Weapons List (V1.0)

The campaign/mission doesn’t matter. Only the difficulty does.
The following list shows the weapons that are only obtainable at Intense difficulty or higher.

• M12 RPG Launcher.
  Intense difficulty or higher.
  Mission reward.
  Not from Hidden Cache.
• Type 76 Auto Shotgun.
  Intense difficulty or higher.
  Mission reward.
  Not from Hidden Cache.
• Kramer Assault Rifle.
  Intense difficulty or higher.
  Mission reward.
  Not from Hidden Cache.
• Type 78 Burst Pistol.
  Intense difficulty or higher.
  Mission reward.
  Not from Hidden Cache.
• AM-16 Gruppa.
  Intense difficulty or higher.
  Mission reward.
  Not from Hidden Cache.
• LEM MP11 Stormsurge.
  Intense difficulty or higher.
  Mission reward.
  Not from Hidden Cache.

They are random mission rewards based on difficulty and not from hidden caches.
Hidden Caches offering perks, cosmetics and emotes though.

*EDIT*
* Heirloom Standoff (Shotgun) is part of the Deluxe Edition.