That should have been done away with in this update.
Items with reputation requirements to acquire no longer require that reputation to apply as a transmog appearance, once acquired.
Tides of Vengeance Update Notes
Grandeur, check to make sure you don’t still have the buyback option on the item. It looks like it was purchased at the end of November, but if you haven’t been on the character much, the timer might still exist.
If the timer is gone and the tabard isn’t otherwise showing up in your collection for any other characters I’d recommend submitting a bug report so our QA team can take a look.