Firstly, is it the small sprocket on the drive disk shaft or the large axle mounted driven sprocket you are after?
Then, count the amount of teeth on the sprocket and the width, the find the chain pitch, just measure the centers of the chain pins (inches). the outdoorking website should stock these items.
At a guess I'm thinking the chain adjuster sprocket because it has a brash bush in it, couldn't help myself. If it is the adjuster bush I was told years ago not to bother using the sprocket, just use a couple of small bearings about the diameter of the sprocket together on the adjuster bracket. Never any problems with it since
Greenfield dealer near me told me that that was the replacement part they would supply or for me just go to the nearest bearing supplier and get a couple of bearing which I did. Any bearing supplier will have them just get a couple that fit the bolt on the adjuster and the outside can be whatever it turns out to be