These guys have a big problem.
www.wotif.com.au shows that everything is sold till the middle of the week or later caravan pks included.
Swan valley is a very very very long way to any beach.
Buying the tents easy but have you ever tried camping out of a suitcase? What about the rest of the essentials.... expensive unless you can reuse.
Try Woodman Point Holiday park www.aspenparks.com.au its a kiting beach and has a variety of accomodation. (includes tent sites maybe sci has a camping gear to lend


)
How long are you in Perth for?
Good luck