There is a place on the internet that you can change a video into an mp3 file. So you can go to youtube, find any Korean song that you like and go to this website below, put the url of the video into the box, hit the dirpy button next to it, and then it'll bring you to another page. You go down and it'll have a record button, click it then save it in the place you want and then it will save it as an mp3 file. Hope this wasn't too confusing.. And I hope it helps.
Oh and it's free.