I agree with m.z.a, that a motorcycle is not the best way to get around the city of Istanbul as a tourist.
In addition to Istanbul metro, buses, and taxis, to get around the city, consider a scooter rental inside the city.
But you could follow m.z.a's advice while visiting Istanbul, and still rent a bike in Istanbul when you're ready to leave the city.
Along with m.z.a's Antalya suggestions, there are also BMW rentals available on the southwest/ Aegean coast in Gocek, an easy domestic airflight from IST to Dalaman airport, or some direct flights from EU gateways to Dalaman:
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