shanime_panda - Thank you for looking. ^^
JeffT - Hm, no, I don't believe it was the kumoricon merch table. This guy had at least 2, if not three long tables for his booth, and an entire table (or 2) was filled with rows of cat ears in different colors. Some were neon, some were glittery, and they all had tufts of feathers in the ears. The assortment was quite astonishing. I believe they were 10 or 15 dollars a pair. He also had other anime merchandise, but I do not recall any Kumoricon merchandise there, so I don't think it was the kcon table.
Thank you both for your help. ^_^