I have confirmed this assuming that the patch of shrubs is regarded as growing naturally. If the seeds have blown in from a garden nearby, there are several small-leaved Olearias it might be. It might be a good idea for someone with a collecting permit to take a flowering piece to the botanic gardens, which I believe will be open again today.
Thanks Betty - Yes this is the first record of this shrub in the Canberra area - would be great if a specimen could be collected.JenniM were teh plants of different sizes?