No decent large scale maps are available, as the Turkish military large scale maps have restricted access.
Small scale maps are obtainable from the Army at Harita Komuntanligi, Dikimevi, Ankara.
(Ask for the Tortum sheet of the 1:250,000 series, cost 13 dollars for foreigners, about 5 million for Turks.)

B/W sketch maps are obtainable from:
Tourism Ministry leaflet, Mountaineering, or download from this site.