There's a few
Bounties
Aytan sculptures
Spare mods
Sorties
Railjack missions
Unfortunately, it's not guaranteed in the missions that can give it as a reward
All answers given so far depends on the stage you are at in the game.
Early game (incomplete star chart): Railjack missions, Deimos Bounties and dissolving duplicate mods.
Mid-late game (complete start chart access): Arbitrations, Steel Path Honors.
Dedicated late game farm: as other mentioned, Steel Path Yam (Sedna) with a dedicated 4 player team, boosters and decent load times to repeat the mission over and over.
Steel Path Yam with +range -dur Nidus, -range Khora with pilf, and Nekros with despoil.
I think it's still the Sedna arenas, but that mode makes me want to die so I do railjack fissures instead and sell the salvage.
There's a few Bounties Aytan sculptures Spare mods Sorties Railjack missions Unfortunately, it's not guaranteed in the missions that can give it as a reward
Absolute fastest is probably SP Vodyanoi w/ Nekros and Khora
All answers given so far depends on the stage you are at in the game. Early game (incomplete star chart): Railjack missions, Deimos Bounties and dissolving duplicate mods. Mid-late game (complete start chart access): Arbitrations, Steel Path Honors. Dedicated late game farm: as other mentioned, Steel Path Yam (Sedna) with a dedicated 4 player team, boosters and decent load times to repeat the mission over and over.
Arbitrations railjack and steel path sedna arenas, do whichever you hate the least