Lab Rats began with episode 0, the trial run, on Oct. 17, 2005. As far as I know, the last published episode was was July 3, 2012. Over the years they hosted their videos on several sites. In seven years, things change: the software you are using, servers, files can get lost or damaged. Stuff happens.
Luckily, it seems they moved all the episodes to YouTube (click for an index) before everything got lost in the ever changing Internet.
The course notes include a lot of links to articles and searches to encourage you to find out more about whataver topic interests you. But videos are so much more fun, and there are a lot of video links. The Lab Rats guys are a bit zany, but that doesn't mean they aren't informative.