In this guide, you will come to know where to farm for Sovereign Outcast in Warframe.
Sovereign outcasts can drop from killing Kuva or Tusk heavy gunners, but it is preferred to farm the Kuva version, which you can find by running missions on the Kuva fortress tiles/planet.
You can run the missions with many enemies spawns in them, so survival, mobile defense, extermination, and defense can have a better chance to spawn heavy gunner.
The mod has around the same drop rate as just about any other stance mod that drops from enemies, so it’s likely going to take you some time before you get the mod. You have to prepare yourself for a long grind if you want to get this mod; you can always buy the mod off someone using plat.
Also, in some cases, heavy gunners will barely spawn, so if you haven’t seen a few by the 5 min mark, you have to extract and come back if you are running a survival mission.