I am a Pakistani national having a valid single entry valid Schengen visa and currently in Istanbul and plan is to go to North Cyprus. Do I need to take visa for North Cyprus? If, yes, could you please guide me from where I can get the visa and if online any website is available?
You don't need a visa for North Cyprus, but that's not because of your Schengen visa, but because no one needs a short-stay visa for North Cyprus except Armenians, Nigerians and Syrians.
So just use your Pakistani passport.