http://workhorse.navistar.com/Default.aspx?tabid=197
The state lookup feature is broken, but if you put in your zip code it should bring up a dealer near you or at least in your state.
Keep in mind since the product got axed in 2010 dealers have been dropping off as the warranty work is done. The only thing left is a small amount of repair work and parts ordering.
I work at a dealer that still has access to Workhorse parts so if nobody local to you is still doing it we can order, you'll just have to deal with the shipping charges.