HP tickets??

You can book them online for Carousell in Cannington or for Garden City in Booragoon at:
link

or for Innaloo or Morley at:
link

I don't know where you can buy them. but do you know what cinema it is likely to be shown in Perth? If so check their website it's bound to have some information on it or go in to the cinema and ask a member of staff if they know anything. I hope my conselhos helps.