Stating the obvious here, but with the current situation, I shan't be visiting second-hand bookshops around Melbourne and Victoria.
If you're looking for a particular second-hand book, many of the bookshops I've visited recently sell through Abebooks, or direct from their premises.
So please do support second-hand bookshops by buying online if you can, so that they'll still be there for us to visit on the other side of this.
In the interim, stay safe.