As far as I know it's not being rerun in the US (correct me if I'm wrong). The best way to see The Muppet Show is to check your video store, or the Internet for the Time Life DVDs which have three episodes on each disk.
If you're willing to spend more money, lol, the individual seasons are currently being released on DVD, so far just 1-3. Netflix also has these season sets and the TimeLife DVDs for rental, if you sign up for an account.
Hope this helps, good luck!