After doing some searching it looks like you've posted your question far and wide across many different sites in hopes for an answer! :-)
Although I don't speak Korean I did some relatively deep searching via Google for the D3100 manual in Korean (using things like limiting results to .pdf's in Korean, limiting results to the Korean Nikon site, phrasing my searches in Korean [thank you Google Translate!] with various advanced wildcards, etc.) and couldn't find a single usable result for a Korean Nikon D3100 Manual .pdf. This leads me to on of two possible conclusions:
- It's not available on the web at all
- It's only available in a 'walled garden' section of the Korean Nikon site for registered Korean D3100 owners which Google is unable to crawl.
Either way, at this point I'd have to agree with the answer posted by someone else on one of the other forums you posted this question at:
"The best thing to do is contact Nikon 1-800-NIKON-UX (1-800-645-6689). Since they are the manufacturer, they would be the best place to go to get that information."