the mods are not max rank because this was for people who are not quite in the endgame, but are in the stage where they can kill liches/sisters (where i am)

Mod acquisition:
[Serration]: Can drop from most mission types, grineer, and infested enemies.
[Heavy Caliber]: Can be acquired from corrupted vaults.
[Rime Rounds]: Can drop from C rotation in Tier 2 Spy missions.
[Galvanized Chamber]: Can be bought from Arbiters Of Hexis for 20 vitus essence each.
[Argon Scope]: Can drop from Cambion Drift bounties.
Vital Sense: Can drop from some mission types, and corpus enemies on railjack or orb vallis
Point Strike: Can drop from lua/tier 2 spy, dark sector defense, and cetus bounties. Can also drop from a LOT of enemies.
[Flux Overdrive]: Can drop from enemies in The Index.