You can purchase worms and worm farms from most Bunnings and Mitre 10, though how long they have been sitting on the shelf for and how healthy the worms are Im not sure.
If you have time to wait sitting a bale of hay or straw on a patch of grass over winter you will indeed find the right kinds of worms underneath that you can harvest for your farm. Digging in the garden and finding the bigger earthworms will not have your farm working efficiently though. What your after is the striped tiger worms that eat decaying matter on the surface. Placing a sack of horse manure in a damp cool spot in the garden will also attract and produce a nice bundle of worms to start you off.
SORRY WE ARE NO LONGER SELLING WORMS
Also if you check out your local community or school garden you may find they have a worm farm and you can purchase worms from them.
Also there are a couple of companies online that ship worms. A Google search will soon have you set with some listings of where to buy!
Happy worm hunting!
FOR GOD SO LOVED THE WORLD HE GAVE HIS ONLY SON, THAT WHOEVER BELIEVES IN HIM SHALL NOT PERISH BUT HAVE ETERNAL LIFE.