You go down route 6
They are in cold storage below Driftveil City
yes, you can find him/her in mistrallion cave next to driftveil city.
You need to beat the Gym Leader in Nimbasa to go to the next city, Driftveil. And in Driftveil, you need to beat that city's gym leader to proceed to Twist Mountain.
after you defeat Elsia, go west and meet her at the bridge. you will get lead across a bridge and there you are in Driftveil city :)
Win
Follow the Direct Road if that's not enough for you, Go through the route next to Driftveil City, navigate Chargestone Cave, and there you are at Mistralton City.
Driftveil City
She is in a home in driftveil city once you recive it she tells you a pokemon to use it on the next time you talk to her.
Driftveil City.
it is at driftveil city
somehow
You get it from Bianca in Driftveil City.