Earliest a Mage can get their own focus items?

[NegaStoat]

If you can get a stacked Invis + Invis to Undead placed on you, you can make your way up to the half portcullis location by the tentacle terrors where the first Dark Elf mage spawns and safely summon a pet in that curved hallway near her, and start at that point. In your low 20's, always use Cancel Magic to pull with as it has a greatly reduced aggro area spike that leaves other nearby spawns docile to your pull.

I leveled a magician there from 20 to 26 from that first mage described above to whacking the other mages and elementals in the nearby chamber, then killing the other mage spawns in the Crystal room. Exp was pretty okay during that stretch and I got about 1 focus item per full level of killing, with several of them being repeats that I couldn't loot. As mentioned above the drop rates off of Cazic gators is much better.