Here is a list of all the "official" Megaversal types of magic, excluding those which already have something assigned.
Choices for some of the above seem obvious enough. Korallyte Shaping should use Korallyte, for one. I could see an argument for TW items using Crystal Magic requiring naturally occurring crystal, which hadn't been magically shaped through either Crystal or Stone Magic. Even though it's a little on the nose in terms of cultural appropriation, I've seen enough cool carvings using chicken-blood stone that it and jade would work well enough for Chi-based items. Several magic types might be best suited to requiring fictional materials. TW items using Space Magic might require something from the Three Galaxies, while Demon Magic and Soulmancy could incorporate something from Hades or Dyval.
Suggestions are welcome.