The most helpful response was from the Istanbul Aviation Club at Sabiha Gokcen Airport
www.ihk.org. By the way they have a T34 in their fleet.
No response from Top Air.
Rates seem roughly comparable with European rentals.
Another tip if visiting Istanbul is the Air Force Aviation Museum at the southern edge of Ataturk Airport. There was a great deal of info on early flying in Turkey and they seem to have been blessed with a greater diversity of competing countries' aircraft than most.
As it was the weather forecast was so bad I decided to rent a car- and then had poor enough visibility over the mountain passes to struggle to remain on the road.
I have really enjoyed visiting Turkey and look forward to a holiday there, rather than rushed business trips.