About 5 months ago in November, Costco has 4 different models of 16 inch Squishmallows, but it sold out quickly. I was unable to obtain any, and it seems others had posted online with the same experience. Today, I saw they had 4 new models at Costco, which I was able to obtain for $9.99. 16 inch ones sell for $24.99 online at squishmallows.com. The models at Costco are Tim, Blake (gray recolor of Bop), Zoe (pink color with unicorn horn), and Danny (green color with ridges on back).
Hopefully they don't run out of stock quickly again, but I put YMMV to be on the safe side. You have to call a specific Costco to check inventory. These Squishmallows are branded "Squishy Squooshems" for Costco.