I run into this obstacle when my debugger steps into some classfile without corresponding source. Finding it is often difficult:
You have to search for the sit
Haven't seen a satisfactory solution myself.
I tend to roll my own repo, without Maven (Maven is fine, but it doesn't click with me). I run something similar to the BSD ports system, that is, one big structured tree that contains little Ant build files. These build files either checkout the source of a project, pull its dependencies from somewhere else in the tree and build it (these are for the projects I want to build- i.e., mine) or pull binaries from somewhere else (which might be an external source or my own binaries repository).
The system could easily be extended to pull src jars, but I do that manually now.