Grat not selling Boots of Aid and Comfort

I'm level 5 in a honour mode run and trying to buy the unique magic item "Boots of Aid and Comfort" from the merchant "Grat the Trader" at the goblin camp.

I've taken over a dozen long rest for his inventory to refresh and the boots to appear, but they don't. I've tried checking his inventory when I barter or pickpocket but they're not appearing either.

Nothing on any wiki online suggests the boots would be non-existant in honour mode. Is this a bug? Is there a way to fix it?

EDIT: The wiki says he should always have them available. What is going on?