i have recently bought a vitz, 2002 model. i've driven it around 450 km. i got cng installed in it from al-mubarik. initially it worked well with very less drop in engine performance but then after a while there was a huge drop in the performance of the car. i went back to al-mubarik, they fine tuned the kit and now its working quite well. just yesterday it did 97.3 km on 40 kg cylinder (in city + motorway). top speed on motorway was around 120 kph.
i've found vitz to be a very good car with all the luxury extras and a very smooth ride. local cars are no match for it. as for the spares, i easily found air filter and oil filter. didnt have to search a lot. not sure about rest of the spares since i havent had the need for them yet.
this is my experience so far. maybe other vitz owners can share their experiences and problems they've faced.