Well North of Perth there is some spectacular Salt water Fly fishing,
Everything from Barramundi/ Bones? Permit/ Queenfish through to Sailfish.
But locally in the Perth area you will struggle for good flyfishing I think.
November a good time of year in New Zealand on your way down or back.
Or a pretty good time of year for trout in Tasmania, sight fishing big browns in the highlands.
Check out
http://www.flylife.com.au/forum/default.html
become a member and ask the question there, great bunch of Aussie and Kiwi Fly fishers including some from Perth.
I'm from Sydney so Perth is like a 5 hr flight West of here, but the guys on flylife will help you out I'm sure.
Regards Pogo