She is 19 OST and Humming Piano Songs

Hi does anyone know where I can find the "She is 19" aka. "my sister law is nineteen" ost? I can't find it anywhere. 

Also I'm trying to find songs from dramas with a "humming" and "piano" aspect, any ideas?

Thanks xxx

There are many OST's in that drama right?

Hi, so what I meant was the whole ost, the whole soundtrack. These songs I can easily find, the ones on youtube, but the other ones are impossible to find... in my opinion. Like for example, the instrumentals. 

Thanks :)