The three largest orc tribes are Blackhand, Hallowfang, and Frostspear. That being said there are other smaller tribes, but none that compare to these three.
The Blackhand tribe resides mostly on the eastern side of the Copper Mountains. They share territory with a few nomadic Goliath tribes. Though the orcs are far more numerous that forces the Goliath tribes back in their caves. The Blackhand tribe does however find itself at odds more with the Stonemaul Dwarves. They are constantly being scattered and broken apart by rampaging dwarven patrols who come screaming out of their holes in the mountain sides. At last estimation the Blackhand tribe was thought to be at 10,000 strong, but they are scattered and unorganized. There is a current leader by the name of Yarleth Scafanth.
The Hallowfang tribe resides on the western side of the Copper Mountains, and much like the Blackhand they share territory. However, the territory is not shared with other bands of orcs, goliaths, or any other mountain populace. The Hallowfang tribe resides in much of the crags, and from this large bands of mercenary bandits roam the same lands. The difficulty of the terrain of the crags makes it a haven for small bands and tribes. Often times when a small band of these orcs is defeated the remnants are seen in the roaming bands of bandits. The Skyhammer Dwarfs often root both the orcs and bandits from their homes. The flying mounts of the Skyhammers allow them to get deep into the crags. There is no current leader of the Hallowfang, and the difficulty to become the leader has been tried and failed by many!
The Frostspear tripe lies in the northern reaches of the Ridgeline Mountains. They are the most tame of all the tribes, and often times keep to themselves. They do find themselves at odds with the Frosthammer Dwarves and the roaming barbaric tribes of the north. Often times as the north often settles things, the territory is claimed by those who resided their first. The Frostspear is no different, and of all the tribes they are the most nomadic. They follow large mammal creatures throughout the north, and fell them as they can for food and clothing. In the northern portions of the continent, survival is often prized above all things. It is said that the leader of the Frostfang Tribe once took the breath of an ancient white dragon and survived. The leader is prized above all and the current leader is Fangar Whiteskin.
There are other smaller tribes of note, they are the Burning Bone Tribe, Pale Scare Tribe, and the Half Skull Tribe.