What corpses have shrunken heads in assassins creed brotherhood corpses

On ACB, shrunken heads are not found on corpses in the game, but in treasure chests positioned all over Roma.

You can buy treasure maps from the Art Merchants, and will allow you to see all the locations of treasure chests, there are over 300. After collecting them all, however, I only ever got 2. You need both for a Blacksmith ShopQuest called Exotica, so DON'T SELL THEM!

I did, and never found any more despite numerous thief attacks, lots of pickpocketing and almost infinite assassination contracts...