How was the intonation when you first got the guitar ?
Gibson usually ships with 10s, maybe give that a shot. If you still have problems it
could be the nut.
Good luck.
Maybe you can contact this guy, he was selling one on eBay :
http://cgi.ebay.com/2005-Gibson-Les-Paul-Supreme-90th-Anniversary-Gold-MINT_W0QQitemZ350021796095QQihZ022QQcategoryZ47072QQcmdZViewItem