Go into "Advanced Search" mode. At the bottom of the page is a check box that says "MileagePlus Upgrade Award". Make sure that is checked.
It may be that United has not released upgrade inventory for any of those flights yet.
Oh - And welcome to FlyerTalk!
Last edited by skimple; Aug 21, 2013 at 6:41 am
Reason: forgot to welcome new FT'er