Websites to download/buy kdramas legally

Hello everyone, 

My friend is a big kdrama fan (as am I) and will be traveling for about 6 months without a stable internet conexion... She doesn't want to download kdramas on illegal websites and is looking for an official site where she can buy kdramas (not the dvds, the episodes on mp4 format). does anyone know a website where we can download or buy kdramas ? 

Thank you so much for your help. She is kinda desperate as you can imagine lol.

As far as I know, Viki is a great website and app for dramas... It's not available where I live but that would be a good start. 

Netflix and iQIYI are the best to download and watch them offline.