http://www.viki.com – This site gives you the chance to watch few Korean dramas with Sinhala subtitles.
http://www.gooddrama.net – This Site is really good and gives you many options to watch.
http://www.hancinema.net – You will find some dramas in this site.
http://www.dramafever.com – You will not be able to watch many dramas through this site.
Where to Watch Sinhala Dubbed Korean Dramas