The unit screen has gone does anyone know if you can get a new screen or replacement in Australia ...application for any help

Pretty sure the answer is no. Autohelm is now Raymarine and you cannot get screen replacements for old Raymarine units.
Ilenart
Found some further info on the old Raymarine site, saids the ST50 is no longer repairable. Looks like the new Raymarine i60 is compatible
forum.raymarine.com/showthread.php?tid=4487&highlight=ST50+RAYFAQ%23
Thanks I will look into this by the way you can still buy led screen in USA but you pay a lot on postag