At the moment, I have no solution to your problem because I am busy with other things. However, I am sure you can find a solution using google searching for how to attach sources to java libraries for debugging.
As soon as I have time, I will reply to this post with a concrete solution.
it has been a long time since your post, but since yesterday there is the new jfuzzylite version 5.0 available for download, which addresses the issue of finding sources. It turns out the problem was caused by the Ant script producing a jar file in “release” mode, thereby excluding information like the source file.