Question

Or do I have to get two arcanines and bring them to the daycare.

Answer 1

Nope, there are no Growlithes in Pokemon Black. You are going to migrate an Arcanine from D/P/Pt or SS/HG to Pokemon Black using the Poke Transfer, then breeding to get it. Note, that to use Poke Transfer, you need to have 2 DS'. Hope this helps...