go to Codex > Dictionary > Sets. look for the ones that increase MP.
also, to make your Mana Shield more effective, some All Resist will help a lot when using Diffusion Talent (adds All Resist x 10 per Rank to reduce damage done to your Manashield) and Barrier Talent reduces Mana lost by 1.5% per Rank (Barrier 40 means you lose 40 Mana for every 100 damage your Shield takes).
For me skullshields is better than manashields and, it is a way stronger from Warriors shieldwall too. Shieldwall only last 4seconds and, had long cool down. While skullshields only disappear if you loss 10%hp and, had a short cd. But, yet I’m still trying to experiment manashields with “Energy” + Electrified or, “Equivalence” with bunoses from druidic and, permafrost with “Harmony” maybe it’s a tough build. I don’t choose alchemy for dmg reduction because, while your mp had still a lot but the HP was scratch out in my opinion
For the sets that adds mp. Cosmic Power, Aetheral Drain, Spell Sword, Cerebral Vortex and, Satyr’s Spirit. You needed adding mp affixes too. Wearing all EL Aetheral Drain will suit it best except the armor but, it only climbs div4-5