You might have better luck getting Korean Air award seats on the LAS-ICN flight, then connect to the TYO airports. I have found LAS-ICN was available when LAX-ICN is not.

You can get some sense of award availability by checking KE's website. If the day is not green, it's unlilkely Delta can get you a seat.
http://www.koreanair.com/local/na/gp...p_seat_ifr.jsp

Here are the blackout dates I have for KE:

December 07, 2012 to January 06, 2013
February 07, 2013 to February 12, 2013
March 01, 2013 to March 03, 2013
May 17, 2013 to June 30, 2013
July 19, 2013 to August 25, 2013
September 14, 2013 to September 23, 2013
October 03, 2013
October 05, 2013 to October 06, 2013
December 07, 2013 to December 31, 2013