Samba is available via anonymous ftp from nimbus.anu.edu.au in /pub/tridge/samba/. If you don't have anonymous ftp access then use ftpmail (http://www.cuhk.hk/guides/earn/ftpmail.html) and get the file samba-latest.tar.gz. The current version is 1.7.07, but that will probably be out of date by the time this is printed.
Samba will probably appear in upcoming versions of the Slackware and Debian distributions. It's also likely that you'll find it on the major Linux archive sites such as tsx-11 and sunsite.