I remember getting a few while farming the Derp hive in Homestead’s fields for Battered Shells.
Your best method though will be crafting them at a Blacksmith - bits and pieces for them like Scrap, Cracked Lodestone or Scavenged Plating can be bought from vendors. Isaiah in Homestead is a good source and is right next to where you spawn in at Homestead so can be checked per session quickly.