I’ve come across this before. Cat go for all sorts of weird & wonderful couplings for bulk grease, often buying whatever the lube system manufacturer (e.g. Groeneveld) use as standard on their tank. Shown as Item #15 above.
My first suggestion would be to take whatever grease coupling that suits the grease gun or bulk fill method the customer is using and buy a male coupling to suit that. All that’s needed then is to get the correct fittings to install the male half of the coupling in the grease reservoir in place of #15.
From what I remember Banlaw did some pretty handy bulk grease couplings for exactly that purpose. in 1/2" or 3/4” NPT if my memory serves me correctly. Their web site would be my first stop. Seeing as the OP is based in Oz they would be my first call.
The Banlaw Grease Transfer Coupling (GTX) represents a step-change in safety and performance.
www.banlaw.com