I've been searching for a UK supplier of 'Heki' scenic products - in particular their 'static' grass fibres - for ages without success. Finally I've discovered Blackwell's of Hawkwell which stock what appears to be the full range of Heki products in their online store.
In MRJ 78 (1995) Martyn Welch describes how he uses a blend of Heki mid green (3361) and winter green (3363) to create a soft green late-August shade. They're availablefrom Blackwell's here.
I also like the look of the Wild Grass and Heki Flor products for simulating longer grass and foliage respectively. These are also available from Blackwells.
UPDATE: The links above go to the trade website. The consumer website is http://www.westminster-miniatures.com/products.php?cat=321