Hi guys! Yeh, I finally managed to get a direct replacement battery for the Cappo after a bit of research! It's from a specialist supplier here in Perth; and they delivered and swapped it around it while my car was parked outside my home. How good is that?
And the satisfying part is that it's just a 1-to-1 direct swap and I didn't have to change the terminals, which is great!

Now I know who to contact when I need a new battery for my other two
kei cars.
Kei cars were never sold here in Australia which is why getting even a simple item like a new battery is so difficult! All the
kei cars which are already here were private imports brought in by collectors and enthusiasts.