I'm not sure I understand why this is a problem. SBT, leiningen, maven and pretty much every other build tool on the JVM supports publishing source jars. I think SBT even does it by default. Nearly all of the open source projects I have worked with on the JVM publish their source jars (Grails used to not but even they do now).

Are you running in to a lot of projects that don't publish their sources?

Also, SBT can use use other SBT projects in github repos as depedencies: http://alvinalexander.com/scala/using-github-projects-scala-...