Baz,
Most everyone here is familiar with Astromart and its a good
source for scopes but its hard to flog them as we're so far away.
This forum has a "Buy & Sell" section that's very active and would be my first choice.
Sirius Optics, Star-Optics and Myastroshop, dot coms, are all dealers in the northern area and all, I believe will take used gear - though it's worth checking.
OzScopes - I don't know about. Their prices actually seem MORE expensive than a bricks and mortar dealer and while I believe they have a good rep for service, would probably stick to the main guys.I hope that's useful. You'll love Cairns at this time of year.
I was born in Vancouver BTW and have family & friends in Calagary - though I never got used to the winters!
PM me if I can be of any help.