This guide will let you know where to get Ammo Mutation Mods in Warframe.
The Ammo Mutation Mods can Drop as a C rotation reward from tier excavation missions, which are excavation missions on Earth, Venus, and Mars.
C Rotation rewards for excavation missions drop every four rounds or four fully completed digs, so 4, 8, 12, 16, etc., rounds/completed digs will drop C rotation rewards. Since you’re going to be running Tier 1 Excavation Missions, the only thing you might get other than the ammo mutation mods is Relics on C rotation, at least.
