Mall of Istanbul is pretty large and mostly aimed at rich Arabs so you can find high-end merchandise. There are quite a lot of brands local and foreign. But it's kind of in an industrial zone of the city, right next to probably the single most used highway interchange in the whole country, gets jammed up 24/7. There are other malls in better locations So maybe just hang around in Istiklal Street in Taksim, maybe Laleli, or Bagdad Street in Kadikoy (Anatolian side), Nisantasi etc. I've also found this 2 year-old article about certain stores, 6 out of 7 is in Istanbul. If you're feeling like going on an adventure, getting lost trying to find them.