It's the same one as for K7, K5 and probably other recent models.
model name is MF-60, which should help you google.
I prefer the divided one, ML-60 - easier to see if you're shooting level.
Adorama has them for a start.
https://www.adorama.com/l/Photography/Camera-Accessories/Pentax~Focusing-Screens
Also try calling Pentax distributor in Australia.
C.R.Kennedy & Co. VICTORIA Phone: (03) 9823 1555
---------- Post added 06-18-20 at 15:54 ----------
Oh, yeah. The price seems high, but they come with a special tweezer tool and storage box.
Just a warning, if you touch the focus screen with your finger (or anything else) IT'S RUINED. There is no way to clean them and they're really delicate. So set yourself up in a clean area and take your time to do it carefully.