I've been running MailScanner for years and years, and I have never seen a mailscanner.sh.sample (it is not in the port's file list either), only the usual sample files in /usr/local/etc/MailScanner/. The starting point should be MailScanner.conf in there. There should be a regular start file in /usr/local/etc/rc.d/, enabled by 'mailscanner_enable="YES"' in /etc/rc.conf, along with some adjustments that need to be done for Sendmail (changing the incoming mail queue for MailScanner to investigate).
Maybe FreeBSD 6 needed .sh files in /usr/local/etc/rc.d (don't quite remember when that was deprecated), but the ports system should generate those for you. In fact, I rummaged around a three year old backup of a mail system and found a 'mailscanner.sh' start script. This was on a FreeBSD 5.5-STABLE. Anyway: installing the mailscanner port must put a 'mailscanner(.sh)' script in /usr/local/etc/rc.d for you, or else something's gone wrong.