As you might expect of an East Asian country bristling with eager mechanical engineers, South Korea has long had a bicycle industry - most notably featuring Samchuly, based in, wait for it... Gangnam-gu in Seoul - ride that pony! In that Korean (and bicycle industry) way, Samchuly shares the same corporate ancestry as Kia Motors - but many of the famous (infamous?) South Korean Chaebol have also dabbled in bicycle manufacture at one time or another.
I have found it harder to uncover the history of bicycle parts manufacturers in South Korea. The only derailleur manufacturer that I am aware of is Samlip. And the only South Korean derailleur that I have found is the, slightly underwhelming, pressed steel, Samlip Tiger.