I am looking for a website which shows when the next fireworks in
either circular quay of darling harbour in Sydney are

Danps,
    
I did a search for "fireworks" on www.darlingharbour.com.au and my
search yielded 4 results. 3 of the 4 events have already taken place.
The next event featuring a fireworks display is "Fiesta" - Australia's
largest annual Latin American and Spanish festival.
     
"The carnival - which kicks-off at 6.30pm on Friday 29 September and
includes a fireworks spectacular at 8pm - hosts Australia's top Latin
American and Spanish bands and dancers over three days and nights."
http://www.darlingharbour.com.au/sydney-Things_to_Do-What_s_On-Fiesta.htm
    
You may want to bookmark the "What's On" page which has a list of
events and a brief description about each, (though fireworks are not
mentioned for "Fiesta"):
   
"What's On"
http://www.darlingharbour.com.au/sydney-Things_to_Do-What_s_On.htm
   
    
For Circular Quay, I checked the Circular Quay events link on the
About-Australia website -- 2 events are listed but none will have a
fireworks display.
    
Link:
http://www.about-australia.com/events/new-south-wales/sydney/events/in/circular-quay/
  
    
I hope this answers your question.
  
Best regards,
  
jackburton