Well, the way the KOSPI derivatives are set up, the futures are full-sized - there is no mini - so the margin is like US$10,000 per.
Roughly speaking, the options are like minis, as the equity is closer to US$2,000. They are technically the most liquid options in the world, because the spread and commissions are similar to mini futures elsewhere, so they essentially replace futures on the KOSPI.
Why the KOSPI doesn't just develop a mini future, I don't know, but I suppose the success of the options means it's not that important for them.
I think IB pointed out (find the thread on this site) that U.S. residents can now trade the Kospi futures, but not the options.
In any case, the Koreans keep their market tightly sewn up, so you wouldn't find non-Korean brokers offering Kospi options (and based on the time zone, how many Americans would trade them? The only ones I know actually live in Korea).
I think, depending on the broker, Americans can contact Korean brokers (some speak English) and open accounts based in Korea. I'd suggest, if interested, you contact a couple of brokers through e-mail and ask.