I can confirm Gaston's Tavern has them and are of good quality. When we lived in California I would often splurge on the very expensive macarons sold in the Downtown Disney area. Better variety there of course but the ones at Gaston's are quite good.
If you would like to share a fun inside joke with the counter-person, ask (knowingly) how many times a day they are ordered as "macaroons". I got one of the loudest unrehearsed and spontaneous guffaws out of the girl there last time.
Side note, the service staff at Les Halles seems to be less inclined towards jovial banter. Actually a pretty dour group of people most days. One might think that if your national culture has been unfairly categorized as rude for the last two-hundred years, one might take such a stellar opportunity to show it to be false, n'est-ce pas? Not that I feel entitled to more than polite friendliness... maybe I should.