Belkzen, Hold of the Orc Hordes is probably your best source
What do you need?
You can find the god here, including a link to the pathfinder wiki for additional pieces of information.
Your most straight forward choice for a spirit should be fire/flames. For a weapon take the favoured weapon (heavy mace) or one of the weapons you get proficiency in as a half-orc. A nice, flavorful feat might be firegod's blessing.
Later I'd suggest spiritual guardian to have your spiritual weapon and similar spells attack at full BAB and deal more damage.
I was thinking spellcaster, too. But an orc/half-orc deserves a decent weapon. More so if he's got 3/4 BAB.
But being a follower of the fire god and not taking the flame spirit seemed strange to me.
The flame spirit's spells are not too bad.
When you have a little more gold fire spirit allows a nice combo: Obscuring mist cast with a smoke stick as an additional component creates smoke instead of mist. With the gaze of flame hex you can see through smoke. So you can hide in a cloud of smoke and cast your spells.
The only thing I REALLY dislike about this spirit is that your familiar becomes vulnerable to cold. That sux. But you can just get an improved familiar with immunity or at least decent resistance to cold.
Those are just suggestions. You can certainly choose a different spirit.