So we know that there are spells called Moon Blade, Solar Blade, Moon Shield, and Solar Shield. Currently they are completely inaccessible by players because they are monster-only spells, usually cast by Moon School and Sun School Monsters. So I had an idea on how to make them somewhat obtainable in item-card form only. Why not make a jewel that players can socket to gain these charms and wards? They could be rare like Hematite jewels currently are, usually only obtainable from specific bosses.
people have asked for these for years now are usually of the same opinion as you; they really want these released. Perhaps now that the Arcanum is teaching other off-school spells, these will make their way into the Astral school
Moon Blade: 
Solar Blade: 