lost and found.
© 2002 David Drysdale
An idea: why not try pootling along to the Lost Property office of the London Underground, and tell them that you left your Gameboy on a Tube.
They'll probably ask which line, so pick a nice popular line like the Circle or Picadilly. Chances are that somebody will have lost a Gameboy on that line, and (slimmer) chances are that somebody will have been noble enough to hand it in. You could take utter advantage of that nobility and get yourself a free machine.