The Washington GLass School offers a basic MIG class. Not very extensive, but enough to get you started: http://washingtonglassschool.com/school/classes.html#1203
For a more in depth class, the Corcorran offers this:
the only co-op metal studio i know of is LandSculpture Studio run by Sam Noto. http://www.landsculpturestudio.com/
they don’t have classes though.