If you've just moved to Sydney, then there's a reasonably good chance of spotting them if you live outside of the city itself and walk around near bushland.
The /r/sydney subreddit is regularly full of reports of people spotting them when the Echidnas are more active during mating season.
I just moved to Sydney and saw them at the Taronga zoo... and I'd never even heard of one before. Strangest little creatures.