I have a LEGO superhero that I painted, and he needs a sidekick. The Sidekick is a boy who has the head of a pigglet! But how do I make a Pigglet head?!?
I would use the head piece from a Gamorrean Guard. This piece can be found in the following sets:
4476 Jabba's Prize
6210 Jabba's Sail Barge
9516 Jabba's Palace
The 1979–1989 Fabuland animals figures have a human body slightly larger than a minifigure, the head, arms and legs move but cannot be removed. The figures are no longer produced but remain quite popular amongst AFOL's. They can still be purchased on sites like Bricklink.
It's a bit late, but in 2020 the Monkie Kid line contains a minifigure-sized pig head:
Another possibility is one of the pig minifigures from the now-discontinued 2016 The Angry Birds Movie theme. For example, see set 75822, Piggy Plane Attack: