I got the following e-mail from their support this morning (1 week after I got the items in the mail, 2 weeks and 2 days after the initial order):
Hi Grayson,
Sorry about this; our supplier was supposed to send us a batch with all
the adapters but didn't, and some had been sent out by the time we
noticed.
We've now received the correct parts and I'm sending out the US and Australia adapters (two of each) in the post today.
Apologies for any inconvenience,
Rory
-- Rory Cullen