Electro-Bolt, Incinerate, Telekinesis, Hypnotize and Security Command are obtained through story progression.
All but one of the others (Cyclone Trap, Decoy, Insect Swarm, Scout and Winter Blast) must be purchased from Gatherer's Gardens with ADAM obtained from Little Sisters.
Note that only the basic plasmids must be obtained, i.e. higher levels of the same plasmid are not required.
The final plasmid is given to you in the area "Persephone", right at the end