Psionatrix of your discipline. Same slot which is annoying, but there's also Torc of Power Preservation. There's the insanely good one in XPH that you can't afford, but also a cheap one in MIC that one gets 5 uses per day but you can afford. Headband of Int +2 or +4. Cognizance crystal.
An Ioun Stone and a Headband of Intelligence do not stack - only the higher of the two enhancement bonuses apply.
Recommend dropping the Ioun Stone and grabbing a Cognizance Crystal or two instead.