The biggest and oldest wizzer gang in Seattle is the Merlyns. They have always been allies of the Finnegan family of the Mafia and in the 2070's they are now fully made men. Many of them dress up like classic images of sorcerers and they take names based on planets and constellations. You can probaly find a bit about them with a net search.
The Spiders of the Redmond Barrens are a bunch of spider shamans that use magic to force people to fight Insect spirits and shamans. Perhaps more powerful than even the Merlyns and scary as hell.
Major wizzer gangs are pretty rare in general because the vast majority of this type of gangs implode fairly fast. It's hard to keep a bunch of arrogant young Awakened in a group like that.