It should've been emailed to you, check your email and the junk folder if not try asking the person in charge I don't know who that is for you to give resend an email with the uac pin and number
NSW HSC applicants
Your Year 12 number was issued to you by NSW Education Standards Authority (NESA). Call 1300 13 83 23 if you've lost your student number.
"Your UAC PIN was emailed to you and it's different from your HSC PIN. If you have lost or forgotten your PIN, go to 'Your application' and click 'Forgotten your PIN?'. You will be emailed a link to reset your PIN. If you're having problems applying, call UAC on 1300 275 822 – from mobiles on (02)9752 0200 or from overseas on +61 2 9752 0200."
^ from the uac site