Codes for additional survivor skins

In the Encyclopedia select the survivor tab.
Go to the last page.
There select the frame with the plus sign.

bloodsplatter
burger
chainsaw
ehre
egg
gore
loot
minigun
monstro
night
nuke
survivor
zombie
zombiedog
zombiehorde

Each code gives you a new survivor skin with a random starter skill.
You can choose one skin by clicking on it to start with in your next normal game.

Codes were found by various people by trial and error so props to them