Hi, I need rear backing plates for a van. I took the van to get the rear brakes fixed and the backing plates are worn out. The repair shop is unsure where to get a pair. I live near Forster NSW.

Depends on the year and factory engine size of the van you can swap with sedan backing plates of same yr or size.
As far as I'm aware mk2 1300 /1600 had same size Small drums Until the induction of the 2.0 in late 1977 where the drums went to the larger size throughout the range Inc 1600 . Sorry I can't measure them for reference as I bin them for disk conversions !

Its a 8/75 Mk1 van and had the 1300 fitted, later I would like to find out about the rear disc conversion but for now I am getting it on the road and having some fun.

Mk1 usually use a borg warner diff, which means it's same thru all mk1 diffs with a back plate. Unless someone has chucked a mk2 diff in there. Only exception is mk1s from '69-71 they had front load diffs as mk2.
You can swap a complete drum brake set from any escort but mk2 has metric brake line threads which is another option