The lack of spots is for two reasons: most activations are 2m and use the local calling frequency, and English is not the easiest language for Koreans, so using the form can be hard.
HF in Korea is difficult as most summits are filled with people on the weekend, but you can find out of the way areas in the activation zones. Also, a lot of summits have military installations, so radios are a good idea.
In Seoul, Ansan, Guryongsan and Yongmasan are easy and there are spots for an end fed or carefully placed dipole. All are busy on the weekend.
Contact Jason HL4ZFA who is always quick to respond and help fellow activators.