The grandparent of missing four-year-old Gus Lamont has been filmed in a scuffle with TV reporters outside court, elbowing one journalist and knocking another to the ground.

Josie Murray faced Adelaide Magistrates Court on Friday, where she was sentenced after pleading guilty to acquiring, owning or possessing a sound moderator - a device more commonly known as a gun silencer or suppressor.

The 75-year-old was charged in February - in the midst of the hunt for the missing youngster - and she entered her plea in writing ahead of Friday's sentencing hearing.

The device was found on the property on January 15 during the massive police search for Gus, who disappeared from Murray's property near Yunta on September 27.

She was fined $10,500 and banned from owning firearms for five years.

Outside court, reporters asked Murray if she was 'pleased' with the outcome, whether she was hopeful Gus would be found, and whether she wanted to say anything about Gus.

She declined to comment as she made her way to a waiting vehicle, shoving outgoing Channel 7 reporter Hannah Foord into ABC reporter Eva Blandis, who fell to the ground.

Murray got in the backseat of a white utility, dropped her phone on the vehicle's running board, and left it there as the vehicle drove off. 

Her wife, Shannon, was nowhere to be seen.  

Instead, she was supported in court by close friend Bill Harbison, who spoke to the media on behalf of the family when Gus first disappeared.

The court was told Murray had owned the silencer legally for several years but did not inform authorities she had it when the law changed in 2017, requiring permission.

Murray's lawyer Andy Ey said it had been a 'very difficult time' for his client.

'To address the elephant in the room, this has been an extremely difficult time for her family - her grandson went missing last year,' he said.

'This is a serious matter, but it is not some James Bond movie where a villain or assassin is walking around corners taking out targets with barely the whisper of a gun.'

Gus was last seen playing in a pile of sand outside the homestead on September 27 last year. 

It has become one of the country's most complex and closely watched investigations.

Police declared the case a major crime investigation and ruled out an abduction by a stranger when they said one of Gus's extended family was now a suspect.

No arrests have been made or charges laid in connection with Gus's disappearance.   

Gus's parents, who are separated, issued a united statement earlier this year describing how their lives had been shattered by their son's disappearance.

'Every moment without him is unbearable. We know someone out there may have information,' the couple said.

'If someone knows what happened, we are pleading with that person - or anyone who may have seen or heard anything - to please come forward. 

'Even the smallest detail could give us the answers we so desperately need.'