If I'm not mistaken, Ticketek usually release a few thousand Grand Final tickets at about 08:00 sharp on the Monday morning before the Grand Final Weekend. Thats how I got my 2003 Grand Final tickets. Mind you, you have to get your arse on the website at 07:55 otherwise you won't get on. (They get thousands of people jumping on the ticketek website at that date and time).
Failing that, just wait another month, I'm sure there will be people in here who's team won't make the G.F. and they'll be quite happy to sell you their tickets. It's far too early yet to start asking people to part with their G.F. tickets, as no one knows who is going to be there.
Pantherjim.