Turgut did some homework for your route after entering Turkish airspace.
Entry point you should request for our route is ADORU
You may have trouble contacting Istanbul Radar frequency at entry point. In that case you can always contact Corlu airport, Frq. 120.37 or 122.10
Corlu VOR frq 115.90 and IST (Istanbul) VOR frq 112.50
Here is the Route
to EKI (Tekirdag city) VOR 116.30
to YAA (Yalova city) VOR 117.70
to BRY after VOR 115.30
At entry point ADORU until YAA maintain 7500 as this is the minimum altitude for the route.
After YAA desend as you like and contact Yenisehir tower 124.20
Remainder for Flight Plans into Turkey. Please don’t miss this.
Please state in section 18 of your plans.
REM/ SELF HANDLING. NO HANDLING REQUIRED