I haven't seen one, but its not for a lack of looking. I think the 22 tooth rear
is as small as you could go. Any smaller and the chain will get wedged between
the hub and the mounting area. (bummer). Thats why I was kinda hoping to find
a rear wheel off of something else that would work and have a smaller sprocket.
Either that or have a 30+ tooth sprocket made for the front. I've kinda decided on
the BIG front sprocket, but havent gotten around to sending out to get it done.