However, here are a few options you could use, depending on the context:
Formal:
* A coven of magicians (This is a traditional term for a group of witches, but can be applied to magicians as well)
* A society of magicians
* A guild of magicians
Informal:
* A group of magicians (This is the most straightforward option)
* A gaggle of magicians (Playful and lighthearted)
* A troupe of illusionists (If they are performing)
Ultimately, the best collective noun to use will depend on the specific situation and the tone you want to convey.