To be honest any decent branded bike will not be remotely close to your budget (9K). Branded bicycles are just like cars and motorbikes, so you can have really expensive ones (made of titanium/ carbon etc) and very very basic ones. You will be surprised at the prices of top non-professional bikes, they can be well over couple of hundred thousand rupees.
Anyway choices available here is very limited. All bicycles sold here are very poor copies and mostly chinese or Taiwanese etc.
Regarding the size, Not sure what you mean by 24", that must be wheel size, as 24 inch frame is going to be huge for anyone unless you are well over 6 feet. If you are 15, than 24" wheels will be too small for you, the full size wheel for all mountain bikes are 26" and thats what you should go for.
Shimano is a Japanese brand, but they don't make complete bikes, just components. So the bike described above is most likely just a copy as well.
Your best bet is to take along someone who knows about the bikes and just go through what ever the shops have and hopefully you will find something half decent. My guess is you will have a much bigger variety in Karachi.
Make sure you are clear what you need the bike for, off-roading, on roading etc. Avoid bikes with shocks etc, they make them heavy and slow and only of use if you are only doing off-roading jumps etc. Avoid big wide tyres , again they make bikes heavy and slow. Most bikes these days will come with 3 sprokes in front and 6 or 7 gears/ sprokets at back, so 18 or 21 speed, most of these gears are useless and never used.