Drifting: VicDrift is the place the go
Hillclimbs: You have a lot of options in Victoria for hillclimbs. My personal favourite is Rob Roy, which has a 'Come and Try Day' on October 5th where entry is only $25! There is also the Victorian Hillclimb Championship, which travel to most of the hill climb tracks around the state for all their rounds.
Motorkhana: Victorian Motorkhana Championship offers all the information you will need for the motorkhana tracks and events. Pakenham and Werribee are my favourites, lots of fun to slide around in there. Rob Roy will host motorkhana day's sometimes as well (but you may need to be a member of MGCC or one of the historic car clubs to get involved in that - usually it's rainy and very muddy meaning lots of fun!)
I haven't done drifting, so can't speak for it. But for hillclimbs and motorkhanas, you don't need much to participate, generally just the CAMS L2S license, a fire extinguisher, seatbelt and helmet is all that's needed. The websites above and the event regulations will tell you what is needed.
If you want more information or anything, feel free to send me a message. I used to race a fair few of them, but got into the officiating side of things more, so have plenty of experience with them