I'm not in Perth, and no knowledge of where to get them locally, but can speak to growing Heliconias in a summer dry/winter wet climate. I am located in northern California, also a medit climate, and the cold hardier species such as H. scheideana, H. matthiasiae, H. spissa, H. latispatha, H. aurantiaca all do fine here, and will take a few degrees of frost and not be killed, if protected by overhead evergreen trees. I would assume that freezes are not your problem, and instead, best culture will require heavy summer irrigation, and planting in shade with wind protection to create the humid environment they prefer. Heliconias look miserable in southern California where fully exposed to the hot dry winds called Santa Ana's which tend to occur in late summer through early winter in the south. The leaves are destroyed and burnt, and I would imagine that hot winds are a regular threat in your local climate as well.

As you are significantly warmer in winter than we are here in San Francisco, you may also have better luck with some of the more tropical species, but I would advise sticking with the ones that don't demand winters above 10C to survive. All the species I mentioned are from southern Mexico into central America and will take abit of winter cold, as it occasionally can freeze at the altitudes these are found in habitat.

My sister lives in Gosford, just north of Sydney, and has some very nice clumps of heliconia psitticorum, Golden Torch, crab claw and rostrata. Given that Perth summers are much hotter, and winters a bit milder, I would expect that you could grow a wide range of heliconias. I also understand that Ravenalla (travellers palm) does well in coastal parts of Perth, and that being a true tropical would indicate that you should have success with a good range of helis as well...

I'm in Scarborough and have a few. Some rostratas in the ground for 3 years sheltered from wind and direct sun but no flowers yet. They go a bit pale and spotty in winter but power on in summer, to the point where I've subdivided new plants off. I also have about a dozen other varieties, mainly cold-tolerant like the angustas (red and yellow), caribea x bihais, orthotrichas, collinsiana. I got all mine from Paradise Distributors in Nambour Qld. They are the only place I've found that will ship to WA because they can get phytosanitary certification. I think they source some plants from another nursery so their range is quite extensive. Just ask them - they're on the web.

I found that there are a few people on ebay who are willing to send to WA by using express post.