Here are the Pokémon that can learn Swords Dance, in Anorith's Egg Group, "Water 3".
Note: Anorith's Egg Cycles - 30 (7,454–7,710 steps to hatch)
Tentacool (via Move Tutor)
Tentacruel (via Move Tutor)
Krabby (via Move Tutor)
Kingler (via Move Tutor)
Kabutops (via Move Tutor)
Corphish (via Level 38/Move Tutor)
Crawdaunt (via Level 44/Move Tutor)
Anorith (via Move Tutor)
Armaldo (via Move Tutor)
So, your best bet is to find a Corphish at Route 102/Route 117/Petalburg City (fishing w/ Good Rod, 20%/Super Rod, 100%)
Note: A bred Pokémon will inherit any compatible Move Tutor moves which it's father knows. Additionally, if both parents know a move that the bred Pokémon can learn via level-up, it will inherit that move.
Though, technically... you don't even have to breed at all. A Move Tutor in the Battle Frontier will teach Swords Dance to your Anorith for 48BP.