The second volume of A Certain Magical Index has recently been released by Yen Press. It is available in paperback, and can be purchased online: Amazon -- Barnes and Noble -- Book Depository

A Certain Magical Index vol 3 Synopsis:
Touma Kamijou is the unluckiest boy in Academy City. Having settled the magical side of his problems for a while, the scientific side of things starts to heat up when Touma’s rival-turned-friend Mikoto meets her own clone. That’s only the beginning of a chain of events that leads Touma and Mikoto to face their deadliest foe yet. Kazuma Kamachi’s smash-hit light novel series continues!