Sorry to say that you will not be able to purchase Unallocated S or G from the Perth Mint. They stopped offering that option to new account holders months ago. You will only be able to buy Allocated Pool and or Allocated. Both attract fabrication fees. Pool account slightly less for storage.
I see the fabrication and storage fees as brokerage. No brainer to have them placed so securely
I too had your plan to target unallocated a few months back, surprised when I went to place my first order as it is still discussed in the PDS. Have been buying Pool allocated ever since.