Welcome to AMTRA Michael, and congrats on buying a bike for the first time in 8 years, what did you get?
Getting on the club rides is easy, have a look at the calendar and pick a ride that you like the sound of, we use a grading system that can be found here,
http://www.vinamtra.com.au/forum/bout-us-information-about-amtra-victoria/ide-standardscornerman-system/Have a look and work out where you fit, then go on a ride that is the level below where you think you are, that way you can work out exactly where you fit ride level wise.
You can go on 3 rides with the club before joining, just to see if Amtra is for you or not.
Being in Berwick there will be lots of rides that are close to your side of town, mainly Neerim, Tynong and Woodside and i run a ride occaisonally at Black Range State Forrest in Murrindindi.
I doubt wether you will get anyone to ride with you tomorrow at such short notice but you never know your luck.
What dirt riding experience have you had and what sort of riding do you like to do?