I had a similar query from an Australian reader, it seems they are much harder to get outside the EU.
Here's my reply; I also heard there are people who buy them up in bulk from Lidl/Aldi then resell them on eBay at a 500% markup…
They regularly turn up at Lidl and Aldi in the UK, in sets of three with two step drills for ridiculously little money.
Aside from that they are pretty easy to source in the UK, for example most of our big towns have a Screwfix:
**LINK**
Bosch do them but the prices are a bit steep, they might be available down under:
**LINK**
I found an Australian supplier – 'Bordo', theirs are unusual in having twisted flutes and index lines for various depths. No prices showing!
**LINK**
It's difficult to spec suppliers for things like these as people have often had them for years and can't remember the source – or the source is no longer there.