Caldera OpenLinux
Bugs: bugs@caldera.com
Security: http://www.caldera.com/news/security/index.html
Support: support@caldera.com
Debian GNU/Linux
Bugs: bugs@debian.org
Security: http://www.debian.org/security/
LinuxCare
While not a vendor they do provide support.
Support: http://www.linuxcare.com/
Support: 1-888-546-4878
NetMAX
Support: support@netmax.com
Red Hat Linux
Bugs: http://developer.redhat.com/bugzilla/
Security: http://www.redhat.com/support/
Support: support@redhat.com
Slackware
SuSE
Bugs: bugs@suse.com
Security: http://www.suse.de/security/index.html
Support: support@suse.com
TurboLinux
Bugs: jht@turbolinux.com
Security: jht@turbolinux.com
Support: support@turbolinux.com
http://www.turbolinux.com/support/