Sageblade of the Archmagus is not obtainable because it requires Nexus Crystals which are not currently obtained from DEing Epics this phase.
This new crafting recipe was added to SoD along with many other revamped crafting epics (e.g. Refined Hammer of the Titans) but it seems to be the only revamped recipe that is not obtainable this phase. It seems like an oversight to not have it available considering it’s low power level compared to raid weapons and the relative dearth of caster pre-raid weapons.