Wa Alaikum Salam.
Brand new Aqua or Vitz might not be available in Islamabad. Almost all such vehicles are imported here as used JDM cars from Japan. Brand New / Zero meter Aqua or Vitz will be extremely costly here.
Why don't you self import a Vitz or Aqua through some reliable importer?
4.5 auction grade car, with Interior & Exterior Grades as A or B, will be very reasonable, and very low mileage 5, 6 or above grades are even considered almost new.
Instead of buying from market, I would suggest to self import one. Many reliable importers are there, and even here on Pakwheels, some reputable Senior Members are there who can guide you in this regard, very well.
You can get in touch with them, especially Umer Bhai from Mycar.pk