from good ol` ebay lol just search for cerium oxide.
its great stuff just mix a small amount, polish the screen then clean off . takes all residue off and gets the glass like new.
i used it as i got some new wipers and they were acting rubbish ( squeaking, juddering) did the screen with this and all was sorted
![jumpmove :jumpmove:](https://www.mk5golfgti.co.uk/forum/Smileys/newsmileys/jumpmove.gif)
was about to send the wipers back!