I have read on reefcentral that you can replace ceramic and steel shafts with carbon fiber shafts that are carried by hobbyshops. I can not find the post but I think it was part of modding either maxijet's or Korellia's. I do remember the site was towerhobbies that carried the shafts and some other impellers.
Here is what I found on their site
I think they are used for R/C boats and cars, but they say carbon fiber is stronger and longer lasting than steel or ceramic. and cheap comparied to buying the whole impeller, I would call around town to hobby shops that carry R/C parts maybe find something local that would only be a few dollars to fix it.
FYI I have not tried this so not sure that the carbon fiber would work just an idea from what I remember reading a while ago