Cepahlon fragments are obtained using a codex scanner. the scanner can be built through the foundry then selected in game by holding f and clicking it. The easiest way to find these is the Ara mission on mars. this is a capture mission, capture the target then that will give you time to look for the fragment. most of the time they are in plain sight and located near the end of the map so I normally go through the map in a linear way and if i havent seen it i go back through all the places. this mission can be repeated and a new fragment will be placed somewhere. It took me 10 minutes overall to get all 3 fragments.