I think both looting and gathering will only harvest items that have been previously dropped. The only way for _new_ items to appear in the game is from Champion/Alpha drops, or through Sages.
And the Sage will indeed, as long as he is in the same region at least, appear to you when you have a certain amount of hours left in your timepool. I'm pretty sure I read that on the Wiki somewhere.
http://wiki.battlemaster.org/wiki/Unique_items
