Troll the auction sites. Check the Shotgun News classified, maybe place a WTB ad. You might want to contact a couple of dealers in good quality used stuff like David Condon in Middleburg, VA or Shooting Investments and have them keep an eye out. Be prepared to pay well, though. Also keep an eye on Simpson's LTD and Cherry's in NC.
Are you completing a collection, or just want one? I know they made a few .308s, but I don't know what configuration they were.
