We have 19 units of the 9V battery clip with 5.5mm/2.1mm plug in stock at our Sydney warehouse.
9V battery clip with 5.5mm/2.1mm plug
We can get a further 100 units from Adafruit Australia.
If you order today we can dispatch this stock between Friday, Mar 29 and Wednesday, Apr 03 2019.
Adafruit's Description of the 9V battery clip with 5.5mm/2.1mm plug
I found these high-quality battery clips. They're molded plastic so they wont tear like cheap clips, and they cover the battery terminals to prevent shorts.
Comes with a 5.5mm/2.1mm center-positive barrel connector, assembled!
Battery not included