WHSmith stock a range of covers - you'll find them next to the ereader display, or you can buy them onllne:
http://www.whsmith.co.uk/CatalogAndS...cessories.aspx
They're quite expensive, though. I recently bought a Kobo WiFi (sounds like the one you mean?) as a present and bought a cover from Navitech, which I thought was a good price for the quality. It was better than the one I bought for my Sony Reader, and didn't seem to block any of the controls
http://www.navi-tech.co.uk/garmin-nu...ories?vmcchk=1