You can get the outfit (Gould's Style) and the hat (Back in Business) at Sarah Winterbaum's (Actually Weintraub) Vault 21 gift shop for 999$ and 99$. It ain't just for pretts, slick, but for protection and class.
Requirements:
All Four Official Story DLCs and Gun Runners' Arsenal
Some credits to: FafnirEtherion who, as it recently turned, is the actual face behind the opened-up "cowboy duster".
DCcharge as always for upscaled textures I used as a basis.
Post S. If you have this Moddb.com , then this outfit will be already presented in the game. They don't overlap though, so you might as well have both, if you want more than one Dick Tracy outfit.