What you are referring to is a working space profile and should reside within your Operating System folders it is placed there when your operating system installed. When you are exporting a file for instance you can select it to tag the exported image. While you are working in Lightroom the application uses AdobeRGB to display images while working in the Library Module, and a derivative of ProPhoto RGB, while working in the Develop Module, you do not have an option to use any other working space profile. See the screen capture which shows where the option to use the profile you are referring to can be selected to export.
That's right. In Windows, sRGB IEC61966-2.1 is hard-wired and always there. You can't even delete it; it will just bounce right back. You'll find it under C > Windows > System32 > spool > drivers > color.