You can get this with a technician character paired with the shield boost skill and tech cores, tools and mods with the max shield stat. It's much easier to get this later in the game when your technician has a higher tech stat and you've researched the ability to craft and reroll gear instead of relying on loot. Bring your character's shield to about 120-160 and you should have no problem reaching 200-300 with the shield boost skill in combat.