Since you'd be starting the circle in Korea, you'd have to be ticketed and originate there too. CX would be your first carrier, so try phoning CX in the US and telling them what you want - they may or may not be familiar with the product, but if they are they ought to be able to arrange the booking for you to collect (and pay for) in ICN.

Otherwise I googled TAs in Korea and found one - http://www.xanadu.co.kr/ - that has RTW info on their website, which bodes well for capability of arranging circle trips too.

Do confirm the price before you get too excited though - a RTW might still be cheaper.