I suspect there is no single reference, but it is implied within different sections. E.g. CAR 5.40 states:
5.40 Pilot acting in command under supervision
(1) A person may fly an aircraft as pilot acting in command under
supervision only if:
(a) the person holds:
(i) a commercial pilot licence or an air transport pilot licence;
or
(i) a certificate of validation that has effect as if it were a
commercial pilot licence or an air transport pilot licence;
and
(b) the person holds an aircraft endorsement that authorises him or
her to fly the aircraft as pilot in command; and
(c) if the person proposes to carry out an activity for which a flight
crew rating is required—the person holds a flight crew rating, or
grade of flight crew rating, that permits him or her to carry out
that activity as pilot in command of the aircraft concerned; and
(d) the person is the co-pilot of the aircraft; and
(e) the operator of the aircraft permits the person to fly the aircraft as pilot acting in command under supervision; and
(f) the pilot in command of the aircraft is appointed for the purpose by the operator of the aircraft.
So you will probably find that if you look elsewhere you will find that if the a/c is being operated with more than 9 passengers on a scheduled service it requires two pilots and that the PIC must be an ATPL, therefore if you do not possess one you would not meet requirement (c) above, for instance. Probably the same with the CIR.
But, the above is just a result of a quick look round the CASA site and not meant to be a definite answer.