Ah you had a Greydwarfs raid. If your Boars were killed they are gone, you will have to tame a new pair of them. If they Boars were not killed it possible they are just wandering around.
If you don't see any new boars around to tame, look for a rune stone that talks about the boars and fires. make sure you do not build fire, torches, or work stations near it.

Clear the surrounding area of live animals and mobs, and in a few days a new set of boars should show up, for you to capture and tame. Keep an eye out for 1 and 2 star boars, they are more resilient and provide more resources. They generally show up further away from the sacrificial stones.