As far as I know this is the first time the name "Akhaten" has been mentioned on Doctor Who on-air. There were not that many episodes with Susan in them, though I can't say for sure that I remember them all (I don't own any of those on DVD). (For whatever it's worth, the TARDIS wikia seems to back up my recollection; it also doesn't show any extended-Whoniverse works that use the name. As always with Wikia, apply your own level of judgement about its accuracy.)
However, the early episodes of Doctor Who were far more about exploring and going interesting places, and much much less about saving the universe from monsters. We didn't really get the action-hero-save-the-world Doctor until Three came along. Travelling to a huge alien market and just going shopping is very much the kind of thing One would have done with his granddaughter.
Also, note that we never saw a television episode with Susan but not Barbara or Ian, while Eleven only mentions being on Ahketan with his granddaughter. While not exactly conclusive, the implication is that he had been to that bazaar before the first episode, and thus we would have never seen it on air.