I saw the movie “A Mighty Wind” and I thought it was very good. Especially the Christopher Guest, Michael Mckeon, Harry Shearer group.
My question is, how come these guys don’t form a band, record music and do some gigs? They are good.
The Folksmen are touring. Guest, McKeon, and Shearer made up the group for a Saturday Night Live sketch. They opened for Spinal Tap (i.e., opened for themselves) when Spinal Tap did a tour. I know I saw just recently some mention of something where the Folksmen did a concert. I don’t know how regularly they do it, but Guest, McKeon, and Shearer have done concerts as the Folksmen.
Spinal Tap does have two albums out, the Black Album from the movie and Break like the Wind. They have also toured as Spinal Tap but I have never seen them even tough I would go.
I heard a story that when they opened for Spinal Tap, the audience booed. They had come to hear heavy metal and didn’t know the same performers made up the Folksmen.
No link for this, just unsubstantiated gossip. 
When the Mighty Wind flick first came out earlier this year, the Folksmen “toured” the TV talk-show circuit and appeared in character.
It talks about the booing of the Folksmen in the Trivia section of the IMDb entry for A Mighty Wind.
Musicat, I can confirm that gossip with more gossip. I saw an interview with Shearer who described opening for his own band. They booed them offstage so they could get back on stage.
Back around 1993, a band I had played in was asked to tour as Spinal Tap’s opening act. This was for the tour that followed the release of ‘Break Like the Wind’. Harry Shearer had gotten ahold of some of our tapes from the bootleg circuit, and called our group’s leader at his day job.
After refusing to believe for about twenty minutes that it actually was Shearer, our leader declined the offer – our band had actually only existed as a studio project, and we all had day jobs anyway.
I feel a certain smug satisfaction upon hearing that the opening act that they had to settle for got booed off…
Yeah, but they did get a movie made about them. Could’a been you at that folk reunion! 
It’s also in the commentary track of the Spinal Tap DVD.