Where can I buy wild rice in UK?

I need to buy some wild rice today and although I've found it for sale online, I can't seem to find any shops/supermarkets that sell it. I just want the wild rice on it's own rather than a packet containing a mixture of wild and other rice (a la Uncle Ben's). Do any supermarkets sell it? Could I use brown rice instead? (I'm making a chicken and squash stew type thing).