Muppets: The Green Album (previously) is now available to listen to in its entirety as an NPR "First Listen".
While elusive on broadcast or cable television, YouTube has the holiday specials you're looking for. John Denver & The Muppets: A Christmas Together (Part 1 2 3 4 5 6). The Christmas Toy (Part 1 2 3 4 5). A Muppet Family Christmas (Part 1 2 3 4 5).
Two MeFi faves end up crossing over: Muppets invade the writers' room at LOST.
Just in time for Easter (or estrous festival, or whatever you celebrate this time of year)... Muppet Rabbits!