World famous hat maker Stetson made a hat which some fans have reworked into an excellent replica of the Man With No Name's hat. From the factory it bore little resemblance but after reworking the crown and cutting down the brim it can be made into a near dead-ringer. Unfortunately Stetson has discontinued this model of hat so you will need to hunt for one.
Jason Skinner sent in these photos of his custom modified Stetson Revenger with an older Straightline Collectibles hatband and it looks fantastic!
I am pretty it was a 70s or 60s stetson revenger. I went through about 5 hats before I found the right one. I had to reshape it and cut the brim. It is tough to get right because you have to get the right one for YOUR head. I have smaller head and face. A lot of hats are too tall or whatever. - Jason Skinner
Basically you soak the thing in water. Run it under the water in the bathtub until it is soaked. Then you reshape it by hand. Sometimes steaming ain't enough. It's not going to hurt it. Once you get it shaped and let it dry, you can spray areas with a spray gun to wet it again to fine tune it. You can get a little brim trimmer from amazon. And you can also buy a pencil roll thing too. But you can also do the pencil roll by hand but it takes a lot of work. I did it all by hand. Instead of using a brim trimmer I used a circle compass and used the metal pointed end to run along the original edge and the pencil end tracing on the inside of the brim. You set it however far you want to trim it. Then cut along that line with scissors. Hope that makes sense. - Jason Skinner
All photos courtesy of Jason Skinner.