There is this death, no parent names given on the index.
Philip Simmons1861 #4860
Aged 56,
Died: Hanging Rock, Tamworth district, New South Wales
This puts his birthdate as abt 1805.
Austcemindex shows a memorial for an
Honor SIMMONDS who died on the goldfields near Hanging Rock in 22 July,1854 aged 31 years (thus born abt !823) which looks a possible. I can't see this death on the NSW index.
http://austcemindex.com/inscription.php?id=1475050NLA newspapers have some mentions of him as Agent for The Mercury - as you have already found. He is also mentioned in The Maitland Mercury & Hunter River General Advertiser, Saturday 21 October 1854 as a person who gave an alarm about a fire.
Not that any of this helps find him before his marriage.

Judith