I assume you mean late May 2017? I would say it would be very unlikely of finding availability, particularly if you don’t hold status with Qantas. If you are Gold, Platinum, or even better Platinum One, I would ring the call centre and ask for their assistance.
Australia to Europe/USA are the most sort after redemptions, and usually get snapped up quickly. Your only hope would be if there is a late cancellation, or more award seats get opened up closer to the date.
If you are like me, and just a Bronze, then generally you need to plan well ahead when trying to redeem points - 11 months ahead.
Another option is expertflyer. I haven’t used that service yet, as I’m usually able to plan well ahead for my redemptions.
If it was me, I would snap up that return leg award seat ASAP, and book an upgradeable one way ticket for the AUS - Europe leg. And then hope you can snag it!
I am sure some other users will have other, and more detailed advice.