Lightning's Blade clan

The Lightning's Blade clan was an orc clan that dwelled in northeastern Gorgrond. It had strong ties to the Thunderlord clan.

After the Horde had conquered much of Draenor, the threat of starvation caused many orcs to turn on each other, clashing in short-lived battles that left hundreds dead. The Lightning's Blade was one of the clans who suffered greatly in these conflicts. When the Horde invaded Azeroth, the Lightning's Blade were left behind on Draenor. After the war, Ner'zhul attempted to reforge the Horde with a promise of new worlds, and managed to attain the partial loyalty of the Lightning's Blade.

Warcraft Adventures: Lord of the Clans
In the canceled Warcraft Adventures, Zul'jin had a banner of the clan inside his shop. The banner displayed a lightning and an axe crossed over a blue background. Zul'jin referred to the clan as ill-fated, and never making it to Azeroth. He heard their initiation rites were so harsh, few were ever able to pass them.

According to Zul'jin, in those rites, young warriors were forced to stand on top of the highest peak of the Blade's Edge Mountains and hold aloft their axes during the thunderstorm. Only those struck by lightning at least three times could join the clan.

Trivia

 * The game manual for Warcraft II: Beyond the Dark Portal refers to the Lightning's Blade clan as an ally of the Thunderlord clan. Nothing more was known about the clan besides this. Some fans believed that the clan's name was simply a mistake, and that the intended reference was to either the Twilight's Hammer clan or Burning Blade clan. In Beyond the Dark Portal, however, the Lightning's Blade is confirmed to exist, and served Ner'zhul's Horde.
 * There are two servers called Lightning's Blade, one US and one EU.

Speculation
The Lightning Sons in Garadar could be all that remains of the Lightning's Blade clan, and judging from their age, they could have formerly been far seers of the clan.