Spares are easily available in Karachi, Lahore and Islamabad. However, they're more expensive than other cars because they are all imported from Japan. And it's always recommended to maintain your car by books (i.e. owner's manual). Gari kabhi tang nahin karegi.
I can hook you up with the parts guy at Dewan Karachi.
Personally, I carry an inventory of 2 oil filters, 2 air filters and 1 set of spark plugs because these are frequently required items. For other parts you can have them within 3-4 days from Karachi.