Best thing to do to acquire as much scrap as you can is to acquire the scavenger trait (gives scrap boost) which is acquired by giving reggie the tarnished ring (random spawn on earth) and get the scavengers bauble (increases amount of scrap picked up by 50%) which can be acquired from completing the red doe bell solution (random spawn dungeon on Yaesha). The Red doe bell solution is (1-5 left to right) 5-4-3-3-4-1-2-3-2-1.
Helped me a lot when trying to speed up this achievement!