I am a Syrian national and I have a Schengen visa valid for two years. I want to go for a visit to Turkey.
My question: can I get my visa upon arrival for 30 days in the airport authority in Istanbul ?
No You cannot get a visa upon arrival,You will have to apply to the nearest Turkish Embassy/consulate for a visa as a Syrian citizen.
Syrian Citizens need a Visa upon entry in Turkey. From official wikipedia visa policy of Turkey: https://en.wikipedia.org/wiki/Visa_policy_of_Turkey
There is no e visa facility for Syrian citizens. From official Republic Of turkey Electronic Visa Application System :