Bring one with you, not a big availability or choice in Turkey, as you will note the Turks are not great with child car seats, most of their kids sit without them or stand behind their parents, even sit on the parents knees in the front. It is always best to try the child in the seat before purchase, and you would not be able to do that.
If you just want it for a hire car and not for long term use in Turkey try Fethiye Lovers they have a wide selection to choose from from age and height.