Are you offering pay? If so then there are probably plenty of java coders (as well as graphic designers and artists) that would be willing to help (We have a work offers forum here on coding forums in fact!). However, if you aren't willing to pay, then you're going to find it hard to get regular people interested without something to attract them.
As far as graphics engines goes, I believe that opengl has a java port
From that you can create your own graphics, engine, etc.