rob, any good builders merchant, like travis or jewsons etc will have plenty of stock. they only cost a few pence each, so dont don't skimp amd make sure your barrier is fully erect, stretched thus keeping the dreaded wrinkles and limp look that some barrier fences have.
any troubles nip round to MB and the sortED clinic hosted by Team JPChenet and a quick consultation will have limpness a thing of the past.