styles are saved in the drawing, if you create a new project/a new drawing you do nothing else then opening a template and not it depends in which template you take to create the next project.
You can use the command _NEW (>>>details<<<) that askes you for a template. Chose a template from Civil (e.g. _AutoCAD Civil 3D (Metric) NCS.dwt or any other that comes with a country kit, if you have one) then you have the styles included that already existed in that template-file (*.DWT). If you take e.g. ACAD.DWT you will only have the "standard"-styles as this template was not created by Civil3D.
If you like to set AutoCAD to automatically start with a Civil3D-template or when you use the command _QNEW (>>>details<<<) you get a Civil3D-template opened as new drawing you have to set the default template file in the options. Start command _OPTIONS, goto tab "Files" and search for template-settings. You can set an existing DWT-file to be automatically used for start, you can also create your own file to be used therefor.
The other option is to import styles to your current project from an external drawing into your current one. Use command _ImportStylesAndSettings to do that (started with Civil3D 2012).
Good luck, - alfred -