Well, it is.
First, in FireRed, LeafGreen, or Emerald, breed a male Corsola with Mirror Coat with a female Mudkip/Marshtomp/Swampert. A baby Mudkip with Mirror Coat should hatch. Then, find the Counter tutor in the game (Celadon Department Store in FR/LG, Battle Frontier in E) Teach it Counter, then migrate it to a Gen IV game. Then, transfer it to Black/White via Poketransfer.
What InfernapePRO said is true also. Get a Wobuffet with both of those moves, breed it with a Shellos/Gastrodon, then breed with a Mudkip/Marshtomp / Swampert.