I saw this advertised this morning via the Ooshies Facebook page:
They also advertise Barbie, Justice League, Marvel, Disney, Avengers, DC & Dreamworks Advent Calendars in this particular ad, but I've seen various others such as Care Bears available as well.
At Big W they retail for $35 from what I can figure out, but the calendars available there are on sale currently for $29.
It looks like each calendar comes with 24 Ooshies, 12 of which are exclusive to the calendar.
Not sure whether this means we can expect new Transformers Ooshies blind bags in the future?
EDIT: Google search found this calendar on catchthedeal.com.au (link) for $50 with more details:
Ooshies Transformers Advent Calendar 2018
Now you can enjoy counting down the 24 days until Christmas with your favorite Transformers Characters! this holiday season create your own Transformers Characters adventures with the all new Transformers Ooshies! open a new window each day to reveal a surprise ooshie and create your own awesome holiday theme adventures! there are 24 pieces in each Advent calendar. Suitable for ages 5+.
Features:
Now you can enjoy counting down the 24 days until Christmas with your favorite Transformers Characters!
Open a new window each day to reveal a surprise ooshie
Create your own awesome holiday theme adventures
There are 24 pieces in each Advent calendar
Suitable for ages 5+