Supermarkets and dairies should have them.

JB HiFi has them.

I'd think most mobile phone retailers should have them.

I didn't look to hard locally, but they had them on the website for $2 with free delivery; arrived the next day
I am pretty sure overnight courier postage cost well more than $2, and the amount I plan to spend will not assist them 

Pak N Save generally does.

trig42:

 

JB HiFi has them.

 

I'd think most mobile phone retailers should have them.

 

You'd think that but you'd be wrong.

Also if you see one of the Skinny dairies around, they should have them. Although my local dairy said they were charging $5

In my experience trying to find one a couple of months ago, Countdown didn't have them, The Warehouse didn't (They have Warehouse Mobile now) but New World did for $2.

My experience was the opposite. Countdown did, New World didn't. Skinny dairy for $5. 

They do seem to disappear quickly. When I needed one recently tried 1 New World, 2 Countdowns and then found one at a Mobil. $8.

Unfortunately, I needed it there and then, so paid up.

:-(

PBTech