You need the service kit. The PN is 90061-0006. Here is a link to the manual for the ballast puppy.
http://www.jabsco.com/files/18220_ballast_puppy.pdf I did a search to try and find that kit. The first place that popped up was a site called Defender.com. Here is just the impeller -
http://www.defender.com/product.jsp?path=-1|311|53460|809302&id=140792
And here is the whole kit -
http://www.defender.com/product.jsp?path=-1|51|299222|121271|316442&id=617826
The only thing I don't like is that the kit doesn't show the impeller and it says it is for the water buddy, so you might want to call and make sure it comes with the kit.