A couple of Gunsan guys on this sight climb. . . Jean in Osan gets out quite a bit, so hopefully he'll see this or I will try to remember to mention it (everyone just FBs these days. . .
Still, you are fairly central and can get to Seoul, Wonju. . . Korea is small so you can get almost anywhere by public transport. Autumn should be winding down, but we're experiencing a rather warm autumn, so. . .
e-mail me if you want more info. . . I may get out this weekend and can help you join in (e-mail in profile). You'll climb if you want!