I was trying to get this from Guh in Frostfire Ridge, following the instructions "Must speak to him in Frostfire Ridge before he joins your garrison." Until I realized that the text was slightly confusing. I thought it was saying that it was unavailable once he was in the Garrison.

The instructions should be changed to say something along the lines of, "Speak to him, to get him to join your garrison, Then buy it from him in your Garrison."