So, I've been wondering this for a while and am finally asking. People have shops selling lots of different custom heads and I'm wondering where the get the heads? How are they obtained? They aren't just player heads are they?
Occasionally, when you die, you drop your head. Once you change your name, heads with your previous name will never change skins.
If you have 1 player, you can do it too. All you do is load which skin you want the head of, die until you get your head, then change your skin and repeat. The heads are static based on what skin you were when you died.