Hey, try the bicycle network aust forum www.bicycles.net.au
There's heaps o melbournians to ask..
Since you're a mtn biker...there's heaps n heaps of events...Give the Otway a shot Or just go & stay in Forrest @ the Guesthouse n ride. perhaps you'll run into jess douglas.
If you want some more mtb stuff check out silentrevolution.com.au
How long are ye gonna be in melbs for?