Hi Bumfish,
ASA has an ongoing recruitment program for the next few years due to the skewed age profile of the current crop of controllers. Several courses will be recruited each year.
Ab initios are selected for either the Enroute or Tower/TMA steam. Some shorter courses will be run for returning expatriots/ex-RAAF/foreign controllers. All recruiting is done online.
If you don't succeed initially, try again because quite a few get through on their second or third attempts - perservere!