Look for "QNH Sources" in the AIP

ENR 1.5-35 para 5.3.2

AIP ENR 1.5 - 35 Para 5.3.2 - QNH Sources

"...These minima may be reduced by 100FT whenever an actual aerodrome QNH is set. Approved sources of actual QNH are ATC and ATIS except when the aerodrome forecast QNH is provided, [u]AWIS[/u] and Bureau of Meteorology (BoM) accredited meteorological observers..."

AIP GEN 3.5 - 21 Para 9.1 - Aerodrome Weather Information Service (AWIS)

"AWIS and WATIR transmit meteorological information from the Automatic Weather Station via a [u]phone number[/u], or at some aerodromes via a VHF radio broadcast..."

Do not forget the time requirement listed in the same paragraph

"An actual aerodrome QNH obtained from an approved source is valid for a period of 15 minutes from the time of receipt.
Note: a METAR QNH does not meet this requirement."

So if you have to conduct a second approach, a new QNH is needed?