Without The PWT
You can get them at gear station for 24 BP. This is the only other way so you will still need battle points to get one either way. There is no pokeball on the ground with one and no NPC will give you one(except for PWT/Battle subway BP salesmen).
You can get a Life Orb at the Gear Station for 24 BP.
Otherwise, you cannot get a Life Orb. You must trade for one.