I have a high-level Corsola I can breed for ya perhaps - mine at present doesn't know Mirror Coat, but Mirror Coat is learned naturally at Lv.48 (changes slightly in B2/W2), so I can send you just the baby if you'd like and you can add the move on level-up; this lets you build up the friendliness as well, at least 5 friendship points per level-up.
Alternatively, they can be caught in Undella Town or on Route 13 with a 30% chance of being found in rippling water (Undella Town seems easier due to the massive coastline and the possibility you may not reach the rippling water before another encounter in Route 13).
If you do want to trade, get back to me. I'll need a little time to get one set up for ya as I have a couple other breeding projects on the go, but I could perhaps have one for Thursday at the earliest.