How did Santa get his elves?

He kidnapped a bunch of children of Siberia. They're very short due to the malnourishment they suffered, living in the USSR, and they're not intelligent enough for skilled labor for the same reason. Santa keeps them in the North Pole because he knows they can't cross the arctic desert without help; it's a form of slave labor he employs because it doesn't require chains.

The slave trade is all and well at the North Pole

They are all his kids from an extra-marital affair he had during his time in middle earth.

[quote]In pagan times, Elves were believed to guard homes against evil. If you were good, the elves would be good to you, but if you were bad, they would play tricks on you. They were known to give people nightmares by sitting on their head while they were asleep.

To keep the elves well fed, happy and out of mischief, people left a bowl of porridge on the doorstep at night.[/quote]

Santa saw their actual nature was good so co-opted them to help him in his work. :)

He kidnapped them from Wonka and threatened their families

He burned down the keebler factory and forced them into slavery

From a magical portal
Or they're from the north pole already

He kidnapped them from Keebler cookies

He and Mrs. Claus have been doing grown up things