How to get more Bull Horn?

So we all know bull horns is needed for us to be able to do mission is Spain. So the question right now is where we can get more bull horns in regular missions. The answer is Vanquish Oelebeth in Nightshade mission. Based on my experience it gives 8-7 bull horns in 1 of 3 attempts. I'm not sure if this is always the case. If you have any knowledge regarding this please post it in the comment area.

Enter Spain

The path of the werewolf is aligned against that of the Turned, and the fate of our races shall always be intertwined in bloodshed. A crisis has arisen in Spain. We have been marked by the Children of the Wolf. We must submit to their ways… or be slaughtered. You must join the resistance, and fight for our freedom!