Zenastara's Magical Curios on Aesry has a 20 mana cambrinth icosahedron necklace holding 20 mana. It also has several 32 mana cambrinth necklaces in the forms of various animals. I suggest adding a 32 face cambrinth icosidodecahedron or buckyball necklace holding 32 mana. While you're at it, how about rounding out the Platonic solids by adding cambrinth tetrahedrons (4 faces) and octahedrons (8 faces) for all the Geometers out there. And why does the cube (6 faces) hold 8 mana?!

Yes, I like geometry.

http://en.wikipedia.org/wiki/Icosidodecahedron
http://en.wikipedia.org/wiki/Truncated_icosahedron