Wizards, as a group, are not the most sociable of animals and any collective noun used should take that into account. Words most often used to describe wizards range from fierce, evil, good, benevolent, odd, powerful, ancient and weird; but never ever sociable. As they are often quite egocentric it is not a stretch to believe that any gathering of wizards would be fraught with disagreements and arguments, so here are a few suggestions:

A squabble of wizards
A quarrel of wizards
A crisis of wizards

The one I think is best is: A contradiction of wizards
This conveys both the fact that they just don’t pal around with one another and if forced to, will not agree on anything.