Hello and thank you for your question.
There are some places on the Atherton Tablelands where it's possible to view Platypus. Tarzali Lakes Aquaculture Centre, and the Platypus viewing platform at Peterson Creek (near Yungaburra) come to mind, but I'm sure there's many more.
If you self drive through this region, I'd suggest stopping in at one of the visitor information centres along the way, as they would have advice on where the best viewing opportunities are at any given time.
I'm not sure if any of the organised tours offer a Platypus Viewing experience as part of their itinerary, as these animals are notoriously difficult to spot reliably!
The tour that this Tripadvisor page was originally set up for no longer operates, but you could contact some of the tours that still operate (just google "Atherton Tablelands Tour") to ask them directly.
I hope this information has helped!