The SBo project does not host the sources of the packages that are built. It is an elegant approach to save space, but occasionally presents problems. Sometimes the source may get moved, renamed or (even worse) it may be an unversioned archive that just changes its MD5SUM.
Normally a user just downloads the source manually or indirectly, by using some of the third party tools like sbopkg, sbotools, slpkg, etc. If the download link is broken, the user has to find the source from some other place, which sometimes may even be called slightly differently (e.g. if you download the source from Debian’s repository). It can be frustrating.
There is a new project, called SBo source archive which aims to offer a public archive of the sources linked to by SBo
.info files. The person behind it, B. Watson, is a maintainer at SBo and here is the announcement on the SBo mailing list. Extensive information (including mirroring) can be found in the corresponding README.
Very nice to have that backup!