Interchange on that backglass seal is '63-'65 Valiant; see discussion
here and
here. Steele Rubber did decide to reproduce it. It's available for purchase, right up on their website.
The backglass gasket in question was not used in Australia. Their '63-'65 Valiants have a totally different backglass, roofline, and gasket.
'66 Valiant owners are still outta luck on new backglass gaskets as far as I know.