Why Australia was the likeliest Surrey-class buyer

If the Surrey class had been completed, could one or more ships have gone to a Dominion navy?

Australia was the likeliest recipient because it could pay for a ship.

A completed Surrey-class program could have opened a Dominion purchase, with Australia the likeliest candidate. The decisive point is funding: Australia could pay for a ship rather than merely request one from British allocations. Imperial fleet distribution depended in part on which government could finance the cruiser.