The Voyagers were one of the Easter Eggs in the beta and launch of Elite Dangerous.
The Solar System was claimed to be modelled as close as possible during development. Someone checked for the Voyagers and found them.
This was mentioned by the developers at launch, and made it into several articles, e.g. this one.
A quick search yielded various youtube instruction videos and reddit threads. A sample quote:
Once you get to the Sol system, fly around for a bit and look for a signal source approximately 2 million LS away. The most important thing to know is that the signal source does not show up in the navigation pane. It's one that you will see out your window, and it will be labeled "Deep Space." You will know it's one of the Voyagers because it will be approximately 2 million LS away. (Voyager 1 was about 2.3 million LS from Saturn when I found it). I hope this helps anyone who was looking for the probes. It is so awesome that Frontier put them in. And, bonus, you can hear part of the Golden Record recording!