a local machine shop should be able to whip one up in a short bit and probably wont cost much at all, just tell them u need a shaft adapter for a 3/4 to 1", and an appropriate key size. if u cut a piece of stock the width of the widest keyway and the length of the keyways depth (ie. for a 1/4 keyway, 1/8" of the key is on the shaft and 1/8" is on the sprocket.) then file the waist on the "T" of the key to match the key way of the sprocket, it will take about 1/hr max to make the key, i had to do this exact same thing a wile ago at work. it works great.