lori l. , who will visit Istanbul soon, asked my recommendation for yarn shops in Istanbul. Well lori, there are 2-3 good brands: Feza (the best yarn), YarnArt and Anchor (in this order). You will see Bravo (which looks so nice, a true eye-catcher), but I don't recommend unless you never wash your knits. One brand is very popular here: Nako. It is quite cheap, they have mostly acrylics. From Nako I suggest only yarns with minimum 50 % wool.
Yarn shops are everywhere here, as 90% of Turkish women are knitting. But, the magic yarn land, a street only with (cheap) yarn shops is in Eminőnű district and the place's name is Kűrkçű Han. Actually, this district of Istanbul, Eminőnű, is the shopping paradise. Words are not enough to describe the experience of shopping here. One day is not enough. Here you can find everything (gold jewelry, yarn, clothing, kitchenware, spices, beading accessories, fabrics, etc) at any price. As a foreigner, YOU MUST BARGAIN. The rule is: you say you like the goods (never offend a Turkish seller by telling him his goods are not nice just to get a discount) but you can't afford this price. You pretend you leave his shop, he calls you back to "talk again", you still say you don't agree and leave again, he calls you again. Patience. This "game" might be tiring for you but is usual here.
It seems lori l. will have a great time in Istanbul.