The final important location in town is the house to the South West. Inside is a woman who will offer two separate trades. At the first trade, she will battle you with the Pokemon you traded her. Win the battle to get a second trade offer.
The girl will offer an Ambipom for your Excadrill. If you don't have any Excadrill, you can find one in many caves all over Unova. They appear in the dust clouds that pop up from time to time. Like most other trades in the game, Ambipom is a very rare Pokemon for this region.
The girl will offer an Alakazam for your Hippowdon. Hippowdon aren't normally found in the Wild in Unova. Either wait for an Outbreak in Desert Resort, or transfer one over from Pokemon Diamond, Pearl, or Platinum. Like most other trades in the game, Alakazam is a very rare Pokemon for this region.