I've only ever seen one person with PD and who had a Service Dog. And I didn't stop to ask him how the dog helped him. But it does strike me that a trained Service Dog could....
Retrieve things for you
Be a friend and a distraction
Might be a real help with freezing episodes . . .
I understand they can be rather pricey. Other than having another element to complicate life, I'd be interested in knowing how they help you.