Are you looking for an early Vietnam era patrol cap? I don't know if there is one other than GI Joe's. Cotswold Collectibles Elite Brigade did have a cloth version at one time. I don't recall how accurate it was.
Or are you looking for a US Army swing cap from WWII? That's going to be tough I'm afraid to find also. I think Elite Brigade might be one place to look. These might have to be custom made by someone like Keith who's business is Kwimm Studios. He can definitely make these but they are custom and are priced reasonably, but not cheap.
Please completely ignore my post if what your looking for is some item I'm unfamiliar with the nomenclature for.