Why not buff one of the existing ones?
Rylai could easily be a 120 AP item, it currently gives 100 AP.
What about Seraph? It wouldn't even need to give 120 AP base, just increase the % from 3 to 4 and it would basically give 120 AP
Actually what if instead, we buff up some of the 80 AP items up to roughly 100 AP status?