You have to have your WvW Provisions Master Ability Line maxed for him to sell HoT stuff... Which takes 55 ability points (wvw level 56). Your mastery points are character specific though, so just send in a toon you'll never wvw with, max that proficiency, and use them to buy all your stuff. Nice trick. Seems a bit odd that the game doesn't suggest this and just gives you a blank tab and the wiki says nothing about the requirements.