need a supply of Oat straw - worcs area

[abina]

My new hay is very rich and will be too much for my lusitanos (not used to eating English hay) and for the ponies and need to mix in some oat / barley straw to bulk up.

Does anyone know of a merchant / farm that supplies oat straw in the worcs/ glos / warks/ oxfordshire area?
Any ideas geratfully received !!

Thanks