There is one here for FS2002 on http://www.simviation.com/fs2002jets38.htm. I'm not sure if it works in FS2004 as it says that it is an FSDS model. If you are willing to pay for it, there is a good Beech 400A made by Eaglesoft (http://eaglesoftdg.com/). I think that the two planes are very similar.