Here is the full list of all 20 Dustoff Z achievements worth 1,000 gamerscore.
Completed the epic difficulty
Completed the normal difficulty
Veteran shooter acquired
Collected a special paint job
Defeated 1000 zombies
Owned a fully upgraded helicopter
Defended the first camp
Defeated 500 zombies
Bought your first helicopter
Defeated the first boss
Escorted the first convoy
Repainted a helicopter
Upgraded a helicopter
Transported a supply to your base
Upgraded a shooter
Hired your first shooter
Saved the first survivor
Defeated 100 zombies
Buy all helicopters
Complete the hard difficulty