Which Pokemon should I teach Earthquake to?

Between my Nidoking, Blastoise, and Dragonite I only have one tm 26. My Nidoking is a ground type and has no other ground moves, Blastoise that needs it to take on electric types, and Dragonite who would just be beastly with that move. Either I need to know which one I should use it on or I need to know a way to find more earthquake tms.