An additional data point, as well as a possible workaround: I am also receiving this error: E: Ignore unavailable target release 'unstable' of package 'xalan' E: Unable to find a source package for I believe that this is because I have ONLY the "deb-src" entries for unstable and testing in sources.list, but NOT the "deb" entries. By adding the associated "deb" entries (and some APT-pinning to ensure that I keep tracking stable) I am able to successfully install source packages from testing and unstable. Removing the "deb" entries causes the problem to reoccur. It seems as if APT is using the binary releases to determine the correct source releases, so if the binary releases aren't there, it gets lost. I don't know much (read: anything) about APT internals, so I have no idea if this is expected/desired behavior. However, In my opinion, it would be nice to be able to specify (only) source entries in order to be able to download different source versions, without needing to worry about pinning or accidentally installing undesired versions of binaries.
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