This guide will let you know where to farm for Epitaph in Warframe.
Epitaph parts can all drop as a completion reward for completing void storm missions on certain rail jack proximas.
The Proxima you will need to be running missions in is the Earth, Venus, and Saturn Proxima’s, though it doesn’t matter which one you run as they can all drop the same parts.
Once in the mission (It also doesn’t matter which mode/mission you pick as long as it’s a void storm). You need to complete the mission as you normally would; also, you don’t need to have a relic or get all ten reactants to get the rewards. You need to complete the void storm mission, and you’ll get the rewards once you’ve finished.