As of yesterday there were 400-500 gift cards remaining in the San Diego area at various Costco locations. They looked it up and rattled off the locations and number, but I didn't take notes.
Yesterday Poway Costco had 45 GC and Merchandise Pickup said they will not reorder. I asked how long they could be returned after they are discontinued and she said "a long time, maybe not 10 years." There are now only 15 left at that location.