Original secondhand Mk3 Ford Zodiac demister grilles come up occasionally on UK Ebay but can go for silly money.
Reproductions appear often on UK Ebay at about £55-60 + postage. The source appears to be Mark Sibley in Exeter UK (Ebay seller mark28576) who ran the now defunct GT40 kit maker MDA.
The link is:- GT40 Demister Grill styled on original on eBay (end time 26-Nov-09 20:29:43 GMT)