The canonical source can be found via anonymous FTP at:
ftp://ftp.sxemacs.org/sxemacs/
There are also snapshots of the current development line available. However, the preferred method to obtain such “snapshots” is via tla (GNU arch):
tla register-archive http://arch.sxemacs.org/2006
tla get steve@sxemacs.org--2006/sxemacs--main--22.1.5 sxemacs