Hello,
Try looking for "Gerd Neumann (jr)" products, there are 10L/mm for 250 per inch for around 35euro, 5L/mm as well, but can be a little more expensive, $55euro.
Steve
Ps.
https://www.gerdneumann.net/
PPs.
https://www.gerdneumann.net/deutsch/...-eyepiece.html (a few shops hold them as well)
Should add Ronchi slides are available in Oz from places like Edmunds optics and Proscitech, but expect to pay between $250-$500+ depending on L/mm and the size/material of the slide.