The biggest rugby test matches on May 12 (v Japan), May 26 (v UAE) will be held at Seongnam http://www.hi-sns.or.kr/ and the best map to find it is http://emap.visitkorea.or.kr/mapurl/45769987-13474668. Kick off time is 1pm.
Moran and Sujin stations are closest. If you take a taxi, show this (성남종합운동장) to the driver.
This is another stadium in Seongnam, so please don't be confussed with Tancheon Stadium.
It is Seongnam Stadium.
From Itaewon to Moran Stn: Itaewon (6th line) - Yaksu (Transfer to 3rd line) -Suseo (Transfer to Bundang line)- Moran
1,550won/ 68 mins