it will take you like 2 hours to find one, or less if your lucky,
here are the steps to follow 
go here : 
http://www.google.co.kr/search?hl=ko&q= ... 98%B8+&lr=
then as this pic : 
 
add a random birthdate  YY/MM/DD
the majority of those ull find will be hided : 
 
keep looking till you find something like this : 
 
when you find it, while u register at yahoo.kr , IT MUST suggest you a nickname wrote in korean, if its wrote only like : ajdbjjj12555 dont use, it wont work !
keep trying till you find one that suggest you a korean name with korean caracters