Spell Focus

Spell Focus item enchantment
Spell Focus item enchantments, including the Spell Focus Mastery, also increase DC of the spell and stack with the feat.

+1 versions
Can be found on randomly-generated weapons, bracers (and not rings) and various named items. Can also be slotted in and such on epic items.
 * Abjuration Focus
 * Conjuration Focus
 * (Divination Focus doesn't exist)
 * Enchantment Focus
 * Evocation Focus
 * Illusion Focus
 * Necromancy Focus
 * Transmutation Focus

Minimum level:
 * Weapons (scepters and such)
 * level 4+
 * level 8+ (foci in two schools, in one item)
 * Bracers
 * level 7+
 * level 11+ (foci in two schools, in one item)

+2 versions (Greater Focus)
Can only be found on named items.
 * Greater Enchantment Focus
 * Dreamspitter
 * Xachosian Eardweller
 * Staff of the Petitioner
 * Epic Spectacles of Spirit Sight
 * Epic Elder's Cap
 * Scepter of Mad Trickery
 * Shard of Xoriat
 * Greater Evocation Focus
 * Black Dragonscale Robe
 * Upgraded Regalia of the Phoenix
 * Epic Robe of Fire
 * Epic Shaman's Beads
 * Greater Illusion Focus
 * Scepter of Mad Trickery
 * Epic Illusionist's Garb
 * Greater Necromancy Focus
 * Staff of the Petitioner
 * Death's Touch (upgraded)
 * Epic Spectacles of Spirit Sight
 * Greater Transmutation Focus
 * Scepter of the Fleshweaver

+3 versions (Epic Focus)
Can only be found on epic items.
 * Epic Conjuration Focus
 * Epic Diabolist's Robe
 * Epic Diabolist's Docent