Not sure if this is the right section of the forum to post this, but I have seen a few posts in the past with people looking for ignition switches. Usually seem to go for a bit more than the £39 asked here if im not mistaken (and from a reputable seller im sure most of you know of) so thought I would post a quick 'heads up'. Could be of use to someone.
http://www.ebay.co.uk/itm/BMW-R100RS-1980-28579-miles-ignition-switch-and-key-/161217752601
http://www.ebay.co.uk/itm/BMW-R100RS-1980-28579-miles-ignition-switch-and-key-/161217752601