Have not seen any of the top-tier plasma sets at CostCo this year - in local stores, or on website.
Doubt they would ever get access to the top of the line sets, although recall them having a 2010 model Pan GT at the very end of last year ( or ? early 2011 ?)
We go to Costco at least twice a month or more and I always make a point to walk through the gauntlet of TVs. The highest level for Samsung and Panasonic sets I ever see there are Costco's proprietary versions of the LED 7000 series (i.e. 7050) for Samsung and the GT level plasmas for Panasonic. In fact, I am pretty sure I've ever seen any Samsung plasmas there, only the LED line.