Having problems finding a repel undead, repel lesser undead, or bane of undead, scroll for use in an "Interesting NPC's" mod quest. Any hints on where such a scroll can be found within reach of a level 18 battlemage-like character? Thanks!

Try buying from the College professors or court mages. If you have the Unofficial Patch, the issue where they only stock Master-level scrolls was fixed.