Ear

s are found on good characters (such as members of the Brotherhood of Steel or Regulators) when the PC has the Contract Killer perk. Daniel Littlehorn from Littlehorn & Associates, located at the Scrapyard, rewards you with 15 caps and bad karma for each ear.

While you cannot kill essential characters, an ear will spawn in their inventory each time they are knocked unconscious. These can then be pick-pocketed from them, yielding an unending source of ears, how a person has an unlimited supplies of ears is something that remains a mystery. (Might be due to Bethesda's scripting which is supposed to add the ear in their inventory on dead but ends up as a pick-pocketing item.)