Kistandalius (or sometimes Blake) in Ars Magicana and Corinna (or sometimes Mpenzak) in Verdistis are good places to buy silver charms. As for finding them, lizard warrior's etc. in the sewers and dragon warriors / trolls in the dark forest are good.
Spellshield works for any magical attack, Aura of Guarding for physical attacks. Spell books for both can be bought; check with the merchants mentioned above.
