Halifax did my last couple of lots and made a great job of them, but they are up in Yorkshire. The Natural Fibre Co are down in the SW so could be more appropriate, although they have a minimum run of about 20kgs (if you don't have that much in one year or of one colour, you can save up a couple of years worth if you store it carefully).
There are also a number of smaller enterprises setting up with MiniMills, so try googling.