Hi all, also from SA, Alberton just south of Johannesburg. Quick idea in case you have not resolved it yet.
Torkcraft sell a 25mm auger drill bit:
Price was around R 270.00
Length is listed as 460mm but it may work with a bit of adjustment to the original design.
Unconfirmed if the 460mm is actual auger part only with the hex drill fitting adding to that lenght in which case even better as the auger part which works at feeding only needs to go from under the hopper to the nozzle which according to drawing is 485mm. Compensation can be made in pipe length or even lengthen the drill by wedling on a good steel bar and truing up on a steel lathe.
We have some lying around our factory will try confirm if length includes shaft or if it’s an overall length.
I’ve seen extruder hacks with shorter out feeds on, and I am pretty sure its much easier to make adjustments to the inside diameter of a pipe to suit 25mm diameter than importing an auger bit of 26mm.
Will get back re: sample ones.