Hi Wren. Try Austain fasteners in Belmont or Coventry Fasteners.
There are Hex Socket with a centre pin or the Torx with the pin.
http://online.coventryfasteners.com.au/OA_HTML/ibeCCtpSctDspRte.jsp?section=3215887
http://online.coventryfasteners.com.au/OA_HTML/ibeCCtpSctDspRte.jsp?section=3215900
I assume that the wall will be built according to AS 2316.1-2009?
