Robot MarketPlace has #35, 10 tooth, 3/8" bore sprockets....no keyway, but it does come with a set screw. Alternatively, you could get a sprocket with a 1/2" bore and keyway from the Robot MarketPlace and then use a nylon shaft diameter adapter with a 3/8" ID and 1/2" OD from Lowes (found in the section with all the drawers of nuts and bolts)
http://www.robotmarketplace.com/mark...sprockets.html