http://www.antiqueautobattery.com/prod03.htm sell Chevrolet batteries in all three types (they used Group 1 and 2) from 1929 to 1953, with the 'DELCO' brand name. I wonder if they have an Aussie distributor (excuse pun)? Otherwise, just in case you have not tried them, I wonder if these people can help?
http://www.chevparts.com.au/home.htm