Going down the Lighthouse Road from the Great Ocean Road to Cape Otway provides many good spots to see some koalas up in the trees. I would say it is impossible to not see any koalas on this road. We ended up parking the car a couple of times to walk around and look out for them. They are usually quite high up in the trees, so pack some binoculars if you have them around.
We were lucky to see a mother koala climbing in the tree with a young one. We also saw a hungry koala enjoying the eucalypt leaves on a low branch. Here it is.