Wish I could help but I rarely listen to any rock. There are a ton of bands though; ballad singers and rock bands seem to be the most common in Korea besides K-pop, so it shouldn't be too hard to find.
I recommend HulKpop. I wouldn't use it to download unless it's something really hard to find, but they have a really big collection. Searching "rock" brings up a ton of results, both popular and more obscure.
Younha is a great pop-rock artist though, she has done a few anime openings/endings as well. I have some electronic(rock) though if you're into that
Oh Jaurim is pretty good, this is one of the few rock albums I've heard and actualyl liked:
https://www.youtube.com/watch?v=gcPTXl2OYsk