It really depends on the type of yoga you want to learn.
For Iyengar yoga, I'd recommend Clifton Hill Yoga Studio: https://www.iyoga.com.au/
For Ashtanga yoga, I'd recommend the Ashtanga Yoga Centre:
http://www.ashtangamelbourne.com.au/
For Shadow yoga, I'd recommend Yoga Moves:
http://www.yogamoves.org.au/shadow-yoga/
Good luck!