I'm not sure whether there are scrolls of "Magic Shield" or "soul shield" in the game. Apart from the cloak of many colours, there are several other items which enhance all (like the infinity helm) or some (like the granite ring for earth) resistances.To increase the character's base resistances, train the magic realms: every four points per magic realm increases the according magic resistance by one point (not absolutely sure about the ratio).
Lastly, the expert skill "Iron Will", which is gained when the character reaches 100 points in Piety, helps the magical resistance. Although a Faerie Ninja will probably never have 100 in Piety...