Turkish substitute for Mascarpone?
The closest Turkish equivalent is kaymak (prononunced like guy-mac but with a k, accent on the second syllable). It is reasonably well available in Turkish mini-marts, although the only available brand may use gums or other thickeners. 

It is not a perfect substitute, and may not whip well if you mix it with cream for pastry-making. But for mixing into a pasta sauce, it will work very well and give you that fat-rich mouthfeel from real mascarpone. 

By the way, I have seen many variants of this sauce. I make mine most commonly with German quark as the dairy component (if you want to try that, ask the Turks for kesmik, but make sure you are getting a wet kind, not a dry kind). So feel free to experiment with any kind of fresh cheese or high-fat fermented dairy, all of them are likely to produce something good, but slightly different in texture and flavor notes. Also, a small tip beside the dairy: instead of all-spinach, try half spinach, half chard (both wilted).