The latest stable version of SCST core is 2.2.1. The latest updates for it you can find it in the SVN branch 2.2.x.
As a complete SCST-based system, you can try Enterprise Storage OS (ESOS). Another similar project is My own Storage Linux OS. NOTE! Both those projects are very early in the development process, so not recommended for production use yet.
The latest development version of SCST core is 3.0. You can download it as well as target drivers and user space utilities directly from the SCST SVN. You can access it using either web-based SVN repository viewer or using anonymous access:
svn checkout svn://svn.code.sf.net/p/scst/svn/trunk scst-svn
Also you can find in the SCST SVN the latest updates for the stable branches. More information about accessing SVN repository may be found here. Or, alternatively, you can download it as a GNU tarball from here.
History of the pre-SVN SCST development is available in SCST CVS repository, which is accessible using web-based CVS repository viewer or anonymous CVS access.