You can buy the yellow striped UK works style but I have not seen it fitted to Aussie cars. Our Mk1 S had plain smooth hose. The Mk2 S had a pattern.
The Mk1 may have been thicker walled because they had issues with the Mk2 style and had to fit an internal spring to prevent it collapsing.
The only document I have that mentions the servo hose is this one for the MK2 S. It doesn't say the MK1 was smooth but it implies it was because the criss-cross style was the way to identify the new MK2 hose.
Attachment:
Brake booster servo hose bulletin YG2S4 501.jpg
Sorry I cant help with where to purchase one.
