Where to find the ancient power TM for Pokemon diamond or Pearl?

Sadly there is no TM for Ancient Power, some Pokemon learn from birth or levelling, like Tangela, Yanma and Piloswine, when they learn Ancient Power and they evolve into Tangrowth, Mamoswine and Yanmega. So catch a Donphan (female) and a Piloswine (male), put them together and you will have a Phanpy with birth move Ancient Power. Go to Bulbapedia to find out more.