If a drama is available on streaming sites like Netflix or Disney Hotstar, and a WEB DL version of that drama is available for download (via Torrent or other methods), they usually come with Korean subtitles (embedded within the file itself.) I don't know if you can access Korean subs if you're not based in Korea, so I don't know if just streaming it directly from those sites is even possible.
And I think Viki has Korean subtitles option for some dramas?