My head is huge. Researching sun hats online led me to discover Henschel hats, and while I was pretty sure that I'd found my match I knew that I needed to try one on my sizable dome before buying.
Located above the Stratosphere Casino (a 5-10 minute walk from the free parking that's available in the Stratosphere Self Park garage), Hat Company of Las Vegas had exactly the hat I was looking for. Not only did they have the color I wanted but also the size I needed. As I debated between the XL and XXL (as I said, huge head) Jim, who was manning the fort, let me know that he could resize the hats for me, and then helped me decide on the XXL after he offered to line the inside of the hat with a layer of felt to make it more secure on my head (originally the XXL was slightly too large). He gave me a bunch of advice regarding hat maintenance and then sent me on my merry way. There was no markup on the price of the hat compared to prices online (in fact I think it was actually slightly cheaper than Amazon's price) and I walked away feeling utterly satisfied with my purchase.
I'm not sure why everyone living in the desert doesn't own and constantly wear a sun hat, and I think that Nevada should issue one to all new residents, but until that happens I recommend you visit Jim at Hat Company of Las Vegas.