If it helps, I think this is the Korean title of the drama you're referring to: 국토만리
But I can find very little info. It's apparently considered to be the first sageuk drama, though! I see dates ranging from 1962 to 1964, so either it was really long, or there's so little info that it's hard to pin down. There are only really short video clips that I can find, and not even photos are easy to come by.
What little I did find:
- It was directed by Kim Jae Hyung, who later directed sageuks Tears of the Dragon and The King and I
- It tells the story of Prince Hodong, son of King Daemusin, as you mentioned above, and the popular folktale Prince Hodong and the Princess of Nakrang (the more recent drama Ja Myung Go is also based on this story)
- The only clips I can find (and I can't even guarantee it's the right drama) are in this video, which is a retrospective of the director's career after his death in 2011
So I think that, unfortunately, there's no way to watch this drama. If it's the time period or story you're interested in, there are more recent dramas you can try. Why were you interested in this drama specifically?