Audax Australia runs a number of rides from 50km-200km+ in the week leading up to the ride. You can register for these rides when you REGISTER FOR THE ALPINE CLASSIC or via their online ride calendar.
The following websites have some helpful tips on training:
Cycling Inform – Download a free Alpine Classic Training Program
If you’re contemplating taking on the ACE250, here are more tips that might help: from a guest post on “The Climbing Cyclist” by Anthony Gugel – http://theclimbingcyclist.com/guest-post-2012-audax-alpine-classic-250km-version/