Hay, straw, sedge or water reeds 16th Century method

‘Da Vinci’s Demons’, a BBC Worldwide/Starz Entertainment TV programme is currently preparing for filming its third series in Swansea.  The series is set in the 16th century, therefore often use traditional methods to achieve the look. They need to get hold of some bundles of hay pre-processing. Hay or straw or sedge or water reeds would do. Can anyone help? If so, please email sally@herefordequestrian.co.uk