You can download it from it’s official website by clicking here
Slackware Linux is the most ancient living Linux distribution, considered the first choice for real, or for old school, hackers and most professional sysadmins, I think Slackware is the safest and faster Linux distribution. Slackware is the most Unix like Linux distribution, sharing basics with BSD.
It’s proven superiority has a high price: Slackware is not user friendly, not designed for that, but if you have free time to experiment and learn, any step using Slackware will probably be a great Unix class. Another important info is Slackware is not maintained by the open source community but by Patrick Volkerding, it’s founder, he releases Slackware’s new versions when he wants, after a couple of years without upgrades users don’t know if the system was or wasn’t discontinued until Patrick suddenly releases it.