The 19-year-old motorcyclist was killed in a crash outside RAF Croughton in Northamptonshire on August 27, allegedly involving Anne Sacoolas, the wife of a US diplomat.
Ms Sacoolas is believed to have been driving on the wrong side of the road when she hit the teenager's motorbike.
The US suspect left the UK after the crash claiming diplomatic immunity, although that protection is under dispute.
Around a thousand motorbike enthusiasts gathered in Northamptonshire on Sunday for a special ride to honour the teenager.
The motorbike convoy made its way through the village of Charlton - following Harry's last ride - and passed RAF Croughton were the crash took place.
Harry's parents - Charlotte Charles and Tim Dunn - were at the event.
Ms Charles said: "It put a smile on our face for the first time in many, many, many weeks. I can't see through my contact lenses very well, because I've been crying so much, but it's been tears of joy, our boy would be so proud."
While Mr Dunn added: "It's got to be sending a message to the authorities that the country are behind us and they want what we want, they want the truth and they want justice for Harry."
In the past few weeks, detectives from Northamptonshire Police travelled to the US where they interviewed Ms Sacoolas and passed the details of the interview to the Crown Prosecution Service (CPS) for consideration.
No charges against the US suspect have been brought.
Mr Dunn's family travelled to the US last month to put pressure on the administration and President Donald Trump to get justice for their son.
However they were told by Mr Trump that Ms Sacoolas would not return to the UK.
The teenager’s parents said they had refused to meet Ms Sacoolas who was also in the White House as they met Mr Trump, as the meeting would have been "appropriate."
However he said the responsibility for telling Harry's family ultimately fell on Northamptonshire Police.
A spokesperson for the family said it is their intention to refer Northamptonshire Police to the Independent Office for Police Conduct for its action during the crash investigation.
They also intend to sue the Trump administration and driver Anne Sacoolas over the fatal motorbike crash.
The Dunn family seek to bring legal action against the US suspect for civil damages and the administration for failing to follow international precedent over who is covered by the rules of diplomatic immunity.