Hi, Ben most of the jewellery supply place's in Sydney should be
able to get one made for you.
or you could just go directly to the guy who makes them.
I.T. Hallmarking Pty Ltd, Templestowe VIC 3106 ph: (03) 9846 1635
It will probably cost you about $120AUD for a stamp, depends on what
you want on it He would be able to tell you how they are made. Chris in Melbourne