I saw your message re Michael John Cater in South Australia when I was browsing the telephone directory.
There is no listing in the phone book of a Michael John Cater, but there is one for a J. Cater (Christian name not given)Perhaps that could be John.Was your Michael ever referred to as John by family members etc.?
Cater is a very rare name in South Australia and there is no-one with the name either Michael or John.
I am forwarding the following though, just in case this may be your person.
J. Cater 38 Lyons Court, Trott Park. South Australia 5158
Good luck with the search.
There are several other people called Cater in the phone book, so hopefully you will be able to contact Michael.