Charmander can get Ancient Power through breeding with Shieldon, Rampardos, Bastiodon and Cranidos
Cranidos can be revived from a Skull Fossil or through trading in Nimbasa City (BW2) . Shiledon is ressurected through the Armor Fossil and also can be traded in BW2.
A worker in the Ice Rock room of Twist Mountain hands out a random Fossil from previous generations, including the Skull and Armor Fossils, once per day.
You have to make sure that the Father is the one with AncientPower (Must have learnt it beforehand) before breeding a Charmander with Ancientpower. :D