There are two that come to mind. AAC makes the 762-SDN-6™ and Mike from Tac Ops make one also. Look up Black Ops or the web page is Tactical Operations
I plan on getting the new SilencerCo Harvester. I've heard great things about it. It weighs 11oz and is $525 at Silencershop right now. Seems pretty hard to beat. .300 win mag rated with a 24" barrel.