I would agree, just use a search engine. You may need something like Autodesk's TrueView to convert the DWG revisions to the version you need if you are using an older version of AutoCAD than the posted DWG standards.
I would tend to start with a location close to your region of the country to help insure similar burial depths, regional suppliers, references to State DOT standards, etc. I've been very impressed with what some municipalities have developed in-house. Some even have lines styles, plot styles, standard blocks and custom menus. Most all of the DOTs are using Microstation, so they'll be limited as a direct resource for AutoCAD.