I bought a clifford one from clifford.net But the finish was just crap on it and the fins had a bunch of burrs, so i sent it back a few months ago..still have not recieved my money back or credit for it yet, so i would try to stay away from them..
I found a valve cover on ebay from the Boat Mercury Cruiser 250, it's a nice aluminum one also way better finish and much cheaper.