Ivory Tower

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Creates a scout tower at a target location.

In its portable form, an ivory tower is a 6-inch-tall model of a guard tower carved from the tusks of a kodo beast.

Source
These can be bought from Arcane Vaults in Frozen Throne.

Kael can find two in Misconceptions, chapter 1 of the Frozen Throne alliance campaign, Curse of the Blood Elves.