Unfortunately, I think you also need to be prepared to accept that there might not be any availability via Velocity for this route. Flights on this route will have to be with partners rather than VA, and in my recent experience that does not bode well for availability through Velocity. And unfortunately, Singapore Airlines no longer flies to/from Athens, so you won't be able to book this route by transferring your Velocity points to KrisFlyer either.
Are you willing to consider getting a flight from Athens to somewhere else to connect with an SQ flight? For example, SQ has availability for next August from Istanbul to Perth in business, for just 53,125 KF miles + USD$292. You'd need to transfer ~72,000 Velocity points to get that number of KF miles, but it's still a lot less than you'd need if a seat was available through Velocity. And I assume you could get from Athens to Istanbul cheaply enough.