Police said on Tuesday the two guns were found hidden under the boot lining of a car that was stopped at Campbelltown in February this year.
One had been modified to be fully automatic but jammed repeatedly when tested, Detective Inspector Steve Taylor of the Crime Gangs Task Force said.
Ongoing investigations resulted in the arrest and extradition to Adelaide of a 33-year-old man from Kellyville, in Sydney's west in July.
He was charged with two counts of acquiring a firearm and was allowed to return to NSW as part of his bail conditions.
Last week a 39-year-old man from suburban Adelaide was also arrested and charged with two counts of supplying a firearm.
He appeared before the Adelaide Magistrates Court on August 5 but did not apply for bail.
He was due to return to court on Tuesday.
Insp Taylor said the shipment of guns was "fairly typical" of bikie gangs and organised crime syndicates.
"Organised crime tends to go hand-in-hand with guns and drugs," he said.