For commercial expeditions you can try the Perth office of World Expeditions or WA’s own Field Touring. Plenty of Perth trekkers and mountaineers have travelled with these guys so you should be able to get references. The technical climbing outdoor shops have catalogues for commercial expedition organisers.
If you’re experienced you might want to try the Australian Mountaineers Information Network to see if anyone is looking for team members. Website is http://www.aminwebsite.com(no dot au).
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