Go to W>W>W>odometergears.com. they have the gear you are looking for.
If you are in there go ahead and replace all three gears. They have a set of all three. The one large gear with the small gear on the back of it needs to be the one for your model. Count the teeth on the small gear on the back of the big one, this will be the one for your model cluster. You can just buy the single small gear if you wish.