Farm The mats in the area you spawn. You can just run in a big circle looking in rooms and whatnot.

If you mean Hadium Flakes then go to patrol, use enhanced tracker or have a Hunter with you, then head through the dirt path towards the Mausoleum head towards the furthest left wall, you will see doorways, these will contain chest, pick up chests, head to the bottom and through the door to the fonts, turn round and go back, loading into a different layer each time to improve spawn probability.