So in a recent alpha exploration incursion I found the three of them, here are some screen caps and the clips of when I found them:
The Arbiter:
https://i.gyazo.com/0990e9f0e9c1b371...ec76450ba4.jpg
https://www.twitch.tv/raevencca/clip...e=7d&sort=time
The Jailer:
https://i.gyazo.com/0d5eeef2e1851bda...fa952460cd.png
https://www.twitch.tv/raevencca/clip...e=7d&sort=time
Rune Sage:
https://i.gyazo.com/484ddf28afc42f0b...e5a7c35873.jpg
https://www.twitch.tv/raevencca/clip...e=7d&sort=time
Some people on the discords specialized in these things accused me of spawning them in in a sandbox, hence the third screenshot with full UI (and everything was done on stream anyways)