The old variety of those are structural and holds the post off the ground. We have them here with 4 little legs on them, very cute but spiders like to hide under there. Ours are 1900s vintage, yours look newer.
This is federation skirting, which you cut on a mitre saw and pin together with a finishing gun. This hides the steel bracket supporting the post.
As these types of skirtings are now manufactured from pine, it would be prudent to treat them before installation as they will be used outside.
Coat the end-grain especially, s this is where the dry rot sets in!
- Scotia, are generally made of timber and used in place of cornice, where your walls meet the ceiling. They are designed to adhere to 2 adjoining surfaces.
Where to get them in Sydney, you will have to go to a Hardware that specialises in joinery type products. A quick flick search on line will find them.
Goodluck with the project,