Thank you so much for interacting with the forums!
To be honest, I don't have a lot of experience with young adult autistic forums/chat rooms, but I would suggest Facebook as a good place to start. I follow a lot of Facebook groups, and in many of them, I see a lot of people on the austism spectrum posting about their experiences.
You could try searching Facebook for some groups in Tasmania specific to young people with autisum. Especially in the current climate with Covid-19, I'd be careful with meeting up with people, but it may be rewarding for him to talk with people who understand him and can relate to his experiences.
Hope this helps! I wish you and your son all the best.
Kind regards, SB