I have a custom hex-shaped tarp made by Lawson Equipment in Cuben. I don't think he's making tarps anymore, but it's really awesome.
Look at ZPacks or Mountain Laurel Designs - they both have tarps specifically designed for hammocks.
One other thought if you're really looking to cut down on your overall weight...See if Ron at MLD will modify his Hex Hammock Tarp to include a poncho-style opening. With a few well-places snaps to shorten it to poncho length you could have a hammock-specific poncho tarp that, if made in Cuben, would weigh around 8 ounces. I live in PA and am only able to weekend trips, but this would allow me to leave my other raingear at home most of the time.