I am a student in Australia and citizen of Pakistan. How can i apply for Transit visa for Hong Kong?

I am a Pakistani citizen. I booked a ticket to travel from Australia to Pakistan with 19hours stay at Hong Kong airport. I could not board my flight as i did not have a transit visa. Now i am stuck as i have to pay heavy cancellation fees for my ticket. I need to travel soon again, as its urgent, kindly please advise me how can i apply for the Transit Visa of Hong Kong so i don't face this problem again. It would be great to know how much time and cost will it be for the transit visa to be approved. Thank you very much.