Those must be the foam ones they hand out on Fremont Street, and the Fremont Street Experience.
http://www.orientaltrading.com/yellow-gallon-hat-a2-13591700.fltr?Ntt=foam cowboy hats
Or this one...http://www.amazon.com/Rubies-Costume-Co-Oversized-Cowboy/dp/B002R9EEXG/ref=sr_1_3?s=apparel&ie=UTF8&qid=1400008361&sr=1-3&keywords=foam+cowboy+hats