Rylin Yeah the posts from Daniel Padilla's Artstation got circulated around in.. January(?)
Those images you sent and the source of them are the only ones I actually knew haha
HOWEVER...
I did start digging for myself and found pretty much "every" source.
Ultimately it trails back to one Discord server that someone named Cashmint posted. Where it houses a Mega Folder full of leaked development docs from Treyarch including, but not limited to, Zombies/these images.
The rest of them come from Daniel Padilla's Artstation...
Which I should note he has since removed all but two images (which I think he simply missed)... The night before the BO6 Direct to be specific. Weird how he could have them up for nearly 6 months then suddenly takes them down but whatever.
I'm currently researching as much as I can about Pre-Alpha Tranzit for the sake of a "project" so I wanted to have as accurate of a source to cite as possible. While your reply didn't provide those exact sources it did lead me down the path that got me to find it. So thank you so much for the reply!