Hi buddy. Not the best member to put you in the picture, Art Andrews is the expert, however I can maybe make it a little clearer. The M or mystery helmets are called this as the origin is a mystery, although legend has it they were cast from screen used helmets. Various vendors supply helmets you can purchase, some may have a relationship to the mystery helmets, however I don't think they are commonly available, unless a member is selling one. As for tutorials, they are out there, I can did out a link for ya if you like, but as the mystery about the mystery helmet is it's origin you won't be making one.
Hope that helps a little buddy.
Also, some one please correct me if this is wrong?