The main Samba site is nimbus.anu.edu.au in pub/tridge/samba/. This is 
maintained by Andrew.Tridgell@anu.edu.au

Mirror sites include:

src.doc.ic.ac.uk:/packages/samba
ftp.demon.co.uk:/pub/unix/samba

There are several others. Give archie a try.

SCO binaries available from:
ftp.markv.com:/pub/samba/samba-1.7.07.exe.tar.gz (built by lance@fox.com)