Hi mortmart, and welcome. In short, you are better off keeping an eye out for another beogram cover, or perhaps a broken beogram that you can switch lids on. You often see broken beograms or even lids alone on ebay. In regards to fixing the scratching yourself, one of the major problems as you said is matching the grain. Emery will put fine scratches in the metal, but it won't blend in with the brushing, especially since you're doing it by hand. A machine is needed in order to give the brushing its look. I suppose you could have a good machine shop try to refinish the surface for you and try to match the other surfaces, but as I said in the beginning it's probably easier just to find another lid. Sorry to disappoint.
Edit: Well look what I just found! The turntable is broken, so if you win you can just ask him to mail you the lid. Remember to tell him to pack it very carefully!
http://cgi.ebay.com/B-O-Bang-Olufsen-Beogram-5000-stereo-turntable_W0QQitemZ230320454498
Austin