The Old Ironsides mod page indicates where the unique ironsides spawn, but when playing with the genesis mod, their spawn location changes.

Zagan: can be found in Squin, as it says on the page of mod (requires 80 relation with Shek and over 100k cats to unlock the recruit dialogue)

Deimos: can be found in The Iron Trail. There is a "Ancient Vault 1" on the island to the west of the coast (To recruit, you need to beat him, capture in сage, and repair by talking to him with a Skeleton Repair Kit and CPU Unit in your inventory.)

Kenji: can be found in Sinkuun. He's at the "Ancient Vault 2", to the north of "Tower of Goats" (just talk to him for recruit)

Marbas: can be found in The Grid. It's in a "Spire" located in the center of the region. (not recruit-able)

P.S I don't know English very well, but I hope that what I have written will be understandable and will help someone.