The prongs are sadly out of stock as there are shortages. He cannot produce what's needed at the moment, hence why it's unavailable.
In a facebook post The Prong wrote
"Regrettably due to the many factors surrounding supply of goods into Australia I have been forced to suspend operations and supply of Prongs until further notice. I have been trying to replenish stock for over year to no avail. There are no alternatives here in Australia who can manufacture at a price that would make them a viable product. Any orders placed in China require a 50% deposit at the placement of the order. Also delivery dates are over 6 months and freight costs have almost quadrupled in the last year. I have therefore decided to suspend trading until such times (if ever) that things are clearer. It has been a tough few months working my way through this. Thank you for your support in the past. I am hoping that in the next 6-12 months I will be able to re-commence. Information on the Prongs is still on the website. But no purchases can be made. Peter"